Science.gov

Sample records for important chemical reactions

  1. Spectroscopy and reactions of molecules important in chemical evolution

    NASA Technical Reports Server (NTRS)

    Becker, R. S.

    1974-01-01

    The research includes: (1) hot hydrogen atom reactions in terms of the nature of products produced, mechanism of the reactions and the implication and application of such reactions for molecules existing in interstellar clouds, in planetary atmospheres, and in chemical evolution; (2) photochemical reactions that can lead to molecules important in chemical evolution, interstellar clouds and as constituents in planetary atmospheres; and (3) spectroscopic and theoretical properties of biomolecules and their precursors and where possible, use these to understand their photochemical behavior.

  2. Studies of Elementary Reactions of Chemical Importance in the Atmospheres of Planets

    NASA Technical Reports Server (NTRS)

    Nesbitt, Fred L.

    2003-01-01

    The paper discusses the following: 1. F + Cl2 Kinetics. Absolute rate constant for the reaction F(P-2) with Cl2 has been measured using the discharge flow kinetics technique coupled to mass spectrometric detection at T = 180 - 360 K and 1 Torr He nominal pressure. 2. Vapor pressure system. The main effort on the vapor pressure system involved the design and construction of an insulated enclosure ("Bakeout Box") to improve the uniformity of heating during the bakeout process. 3. Sunphotometer System. This period saw the completion of the two-channel sunphotometer, its calibration, and two field deployments. 4. Vibrational-to-translation (V-T) transfer rates for light hydrocarbons at low temperatures are important parameters in thermal-structure models of the upper atmospheres of the outer planets and their satellites. However, the required data are either simply not available or do not extend to the low temperatures found in those systems. Because methane is such an important constituent in outer planet atmospheres, we have initiated a program to measure the temperature dependence of (V-T) rates for its relaxation by appropriate collision partners. 5. The central focus of this research has been the vapor phase nucleation and growth of metals/refractory species into small particles and the aggregation of these primary particles into larger structures. These topics are part of the broader goal of understanding the conditions under which interstellar dust grains condense from stellar outflows and how these small dust grains coagulate into larger bodies such as planetesimals or planets.

  3. Microfluidic chemical reaction circuits

    SciTech Connect

    Lee, Chung-cheng; Sui, Guodong; Elizarov, Arkadij; Kolb, Hartmuth C.; Huang, Jiang; Heath, James R.; Phelps, Michael E.; Quake, Stephen R.; Tseng, Hsian-rong; Wyatt, Paul; Daridon, Antoine

    2012-06-26

    New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

  4. Studies of Elementary Reactions of Chemical Importance in the Atmospheres of Planets

    NASA Technical Reports Server (NTRS)

    Nesbitt, Fred L.

    2001-01-01

    The methyl self-reaction was studied at T = 298 K and 202 K and at three different pressures, P = 0.5, 1.0, and 2.1 Torr. The experimental measurements were performed in our discharge flow-mass spectrometer (DF-MS) apparatus. The methyl radicals were generated by the reaction of F with methane. Passing a mixture of molecular fluorine, F2, in helium through a microwave cavity generated the atomic fluorine reagent. The atomic F enters the flow tube through a rear port on the flow tube. The methane reagent enters the flow tube through a movable injector located coaxial in the flow tube. The decay of methyl radical signal was monitored at a mass/charge ratio (m/z) of 15 as a function of the injector distance. To minimize secondary chemistry from the reaction CH3 + F to CH2 + HF the initial [CH4](sub 0)/[F](sub 0) was above 37.0 and typically 100. This ensures a 1:1 relationship between initial [F] and [CH3]. A titration of F with excess Cl2 yields the initial [F](sub 0). Our experimental methodology to accurately measure the mass spectrometer scaling factor, i.e., the relationship between initial signal and [CH3](sub 0) has been improved. Now we measure the CH3 signal decay under exponential decay conditions at low initial [F](sub 0), 3x10(exp 11) molecule/cc, in the presence of Cl2. This minimizes the second-order decay contributed by the CH3 self-reaction and a simple extrapolation of the 1n(signal) vs time plot to t = 0 gives the initial signal. This provides the desired relationship between initial signal at 15 amu and [CH3](sub 0). The resulting calibration is then applied to the observed decay of the CH3 signal at high concentrations of CH3 assuming linearity of this scaling factor.

  5. Chemical Reactions at Surfaces

    SciTech Connect

    Michael Henderson and Nancy Ryan Gray

    2010-04-14

    Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

  6. Chemical Reaction Problem Solving.

    ERIC Educational Resources Information Center

    Veal, William

    1999-01-01

    Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

  7. Chemical Reaction Problem Solving.

    ERIC Educational Resources Information Center

    Veal, William

    1999-01-01

    Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where

  8. Concordant Chemical Reaction Networks

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    We describe a large class of chemical reaction networks, those endowed with a subtle structural property called concordance. We show that the class of concordant networks coincides precisely with the class of networks which, when taken with any weakly monotonic kinetics, invariably give rise to kinetic systems that are injective a quality that, among other things, precludes the possibility of switch-like transitions between distinct positive steady states. We also provide persistence characteristics of concordant networks, instability implications of discordance, and consequences of stronger variants of concordance. Some of our results are in the spirit of recent ones by Banaji and Craciun, but here we do not require that every species suffer a degradation reaction. This is especially important in studying biochemical networks, for which it is rare to have all species degrade. PMID:22659063

  9. Chemical Reactions in DSMC

    SciTech Connect

    Bird, G. A.

    2011-05-20

    DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

  10. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  11. Chemical burn or reaction

    MedlinePLUS

    ... different products that contain toxic chemicals such as ammonia and bleach. The mixture can give off hazardous ... chemicals immediately after use. Use paints, petroleum products, ammonia, bleach, and other products that give off fumes ...

  12. More on Chemical Reaction Balancing.

    ERIC Educational Resources Information Center

    Swinehart, D. F.

    1985-01-01

    A previous article stated that only the matrix method was powerful enough to balance a particular chemical equation. Shows how this equation can be balanced without using the matrix method. The approach taken involves writing partial mathematical reactions and redox half-reactions, and combining them to yield the final balanced reaction. (JN)

  13. Reduction of chemical reaction models

    NASA Technical Reports Server (NTRS)

    Frenklach, Michael

    1991-01-01

    An attempt is made to reconcile the different terminologies pertaining to reduction of chemical reaction models. The approaches considered include global modeling, response modeling, detailed reduction, chemical lumping, and statistical lumping. The advantages and drawbacks of each of these methods are pointed out.

  14. Chemical reactions in turbulent mixing

    NASA Astrophysics Data System (ADS)

    Liepmann, H. W.; Brown, G. L.; Dimotakis, P. E.; Roshko, A.

    1980-06-01

    The combustion facility (H2-F2) is now nearing completion. As of this writing, a high speed mixing layer has been realized in the test section, using high pressure air. This certifies the flow facility down to and including the test section. Preliminary results on the effect of high heat release in a turbulent mixing zone were obtained in the NO-O3 experiment. These results are consistent with predictions based on previously measured p.d.f.'s in non-reacting mixing layers, but in conspicuous disagreements with a variety of accepted model calculations. These results demonstrate again the important influence of the large scale coherent structures on chemical reactions in turbulent flows. The Laser Induced Fluorescence technique has now been extended to allow direct space and time resolved measurements of the reaction products. The first four channels of the multi-channel laser Doppler velocimetry system are essentially completed. The first experiments using this new development are expected in the course of this summer. Digital image analysis of particle streak photography has also been explored as a direct means of two dimensional measurements of the velocity field in a plane. Finally, a prototype system using a 100 element acoustic detector array has been completed. Initial measurements with four of these channels using 300 kHz sound have been successfully made.

  15. Programmability of Chemical Reaction Networks

    NASA Astrophysics Data System (ADS)

    Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

    Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

  16. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1994-01-01

    Quantum mechanical methods have been used to compute potential energy surfaces for chemical reactions. The reactions studied were among those believed to be important to the NASP and HSR programs and included the recombination of two H atoms with several different third bodies; the reactions in the thermal Zeldovich mechanism; the reactions of H atom with O2, N2, and NO; reactions involved in the thermal De-NO(x) process; and the reaction of CH(squared Pi) with N2 (leading to 'prompt NO'). These potential energy surfaces have been used to compute reaction rate constants and rates of unimolecular decomposition. An additional application was the calculation of transport properties of gases using a semiclassical approximation (and in the case of interactions involving hydrogen inclusion of quantum mechanical effects).

  17. Chemical reaction rates and solvent friction

    SciTech Connect

    Hynes, J.T.

    1986-01-01

    The role of the dynamic solvent friction in influencing the rates of chemical reactions in solution is described. Features considered include (a) the bias of the reaction coordinate toward a direction of lesser friction in the diffusive limit, (b) the importance of frequency-dependent friction in atom transfers, tunneling reactions and isomerizations, (c) the dynamic nonequilibrium solvation in charge transfers which leads to a polar solvent molecule reorientation time dependence for the rate, and (d) the importance of internal degrees of freedom in the location of the Kramers turnover for isomerizations.

  18. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    Hugerat, Muhamad; Basheer, Sobhi

    2001-01-01

    Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical

  19. Theoretical study of chemical reactions in solution

    NASA Astrophysics Data System (ADS)

    Yokogawa, D.

    2015-12-01

    Quantum chemical calculations in solution are becoming more and more important in chemistry. Reference interaction site model self-consistent field (RISM-SCF) is one of the powerful approaches to perform quantum chemical calculations in solution. In this work, we developed a new generation of RISM-SCF, where a robust fitting method was newly introduced. We applied the new method to tautomerization reaction of cytosine in aqueous phase. Our calculation reproduced experimentally obtained relative stabilities and relative free energies correctly.

  20. Nanomotors Propelled by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Kapral, Raymond

    2013-12-01

    Molecular motors, like their macroscopic counterparts, consume energy and convert it to work; however, unlike macroscopic motors, they are subject to strong fluctuations and do not rely on inertia for their operation. In this chapter, the dynamics of synthetic chemically-powered nanomotors and mechanisms by which they operate are described. The focus is on motors that propel themselves by utilizing fuel in the environment to generate their own concentration gradients through chemical reactions. Macroscopic diffusiophoretic mechanisms for such motions are discussed, as well as microscopic and mesoscopic descriptions of motor dynamics.

  1. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    Hugerat, Muhamad; Basheer, Sobhi

    2001-01-01

    Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical…

  2. Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions

    PubMed Central

    SUZUKI, Toshinori

    2013-01-01

    Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. PMID:23318678

  3. Learning to predict chemical reactions.

    PubMed

    Kayala, Matthew A; Azencott, Chlo-Agathe; Chen, Jonathan H; Baldi, Pierre

    2011-09-26

    Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

  4. Learning to Predict Chemical Reactions

    PubMed Central

    Kayala, Matthew A.; Azencott, Chlo-Agathe; Chen, Jonathan H.

    2011-01-01

    Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles respectively are not high-throughput, are not generalizable or scalable, or lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry dataset consisting of 1630 full multi-step reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval, problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of non-productive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal (http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

  5. Mineralogical and chemical assessment of concrete damaged by the oxidation of sulfide-bearing aggregates: Importance of thaumasite formation on reaction mechanisms

    SciTech Connect

    Rodrigues, A.; Duchesne, J.; Fournier, B.; Durand, B.; Rivard, P.; Shehata, M.

    2012-10-15

    Damages in concrete containing sulfide-bearing aggregates were recently observed in the Trois-Rivieres area (Quebec, Canada), characterized by rapid deterioration within 3 to 5 years after construction. A petrographic examination of concrete core samples was carried out using a combination of tools including: stereomicroscopic evaluation, polarized light microscopy, scanning electron microscopy, X-ray diffraction and electron microprobe analysis. The aggregate used to produce concrete was an intrusive igneous rock with different metamorphism degrees and various proportions of sulfide minerals. In the rock, sulfide minerals were often surrounded by a thin layer of carbonate minerals (siderite). Secondary reaction products observed in the damaged concrete include 'rust' mineral forms (e.g. ferric oxyhydroxides such as goethite, limonite (FeO (OH) nH{sub 2}O) and ferrihydrite), gypsum, ettringite and thaumasite. In the presence of water and oxygen, pyrrhotite oxidizes to form iron oxyhydroxides and sulphuric acid. The acid then reacts with the phases of the cement paste/aggregate and provokes the formation of sulfate minerals. Understanding both mechanisms, oxidation and internal sulfate attack, is important to be able to duplicate the damaging reaction in laboratory conditions, thus allowing the development of a performance test for evaluating the potential for deleterious expansion in concrete associated with sulfide-bearing aggregates.

  6. Chemical reactions at aqueous interfaces

    NASA Astrophysics Data System (ADS)

    Vecitis, Chad David

    2009-12-01

    Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1) Adsorption of dilute PFOS(aq) and PFOA(aq) to acoustically cavitating bubble interfaces was greater than equilibrium expectations due to high-velocity bubble radial oscillations; 2) Relative ozone oxidation kinetics of aqueous iodide, sulfite, and thiosulfate were at variance with previously reported bulk aqueous kinetics; 3) Organics that directly chelated with the anode surface were oxidized by direct electron transfer, resulting in immediate carbon dioxide production but slower overall oxidation kinetics. Chemical reactions at aqueous interfaces can be the rate-limiting step of a reaction network and often display novel mechanisms and kinetics as compared to homogeneous chemistry.

  7. Spectroscopic and photochemical study of molecules important in chemical evolution

    NASA Technical Reports Server (NTRS)

    Becker, R. S.

    1973-01-01

    The primary broad goals of this research are to investigate (1) the possible reactions responsible for generation of compounds important in chemical evolution, and (2) reactions of compounds important in chemical evolution. In both cases the interest includes molecules that exist in interstellar space as well as those present on or near other planets and those which were thought to be present on or near the primitive earth.

  8. Minimum Energy Pathways for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Walch, S. P.; Langhoff, S. R. (Technical Monitor)

    1995-01-01

    Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives useful results for a number of chemically important systems. The talk will focus on a number of applications to reactions leading to NOx and soot formation in hydrocarbon combustion.

  9. Theoretical studies of chemical reaction dynamics

    SciTech Connect

    Schatz, G.C.

    1993-12-01

    This collaborative program with the Theoretical Chemistry Group at Argonne involves theoretical studies of gas phase chemical reactions and related energy transfer and photodissociation processes. Many of the reactions studied are of direct relevance to combustion; others are selected they provide important examples of special dynamical processes, or are of relevance to experimental measurements. Both classical trajectory and quantum reactive scattering methods are used for these studies, and the types of information determined range from thermal rate constants to state to state differential cross sections.

  10. Chemical reactions in endoreversible thermodynamics

    NASA Astrophysics Data System (ADS)

    Wagner, Katharina; Hoffmann, Karl Heinz

    2016-01-01

    Endoreversible thermodynamics is a theory for the (approximate) description of thermodynamic non-equilibrium systems, which allows us to capture the ever present irreversibilities of real processes. For instance in heat engines the dissipation due to finite heat transport capabilities, as well as the resulting limitations in the energy fluxes, can be incorporated into the theory. It has thus been very successful in closing the gap between observed and theoretically predicted efficiencies. Here an extension of the theory is provided, with which chemical reactions can be included in the formalism. This opens up a wide field of applications for endoreversible modeling and the investigation of dissipative processes, for instance in fuel cells or batteries.

  11. Suppression of Ostwald Ripening by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Zwicker, David; Hyman, Anthony A.; Jülicher, Frank

    2015-03-01

    Emulsions consisting of droplets immersed in a fluid are typically unstable and coarsen over time. One important coarsening process is Ostwald ripening, which is driven by the surface tension of the droplets. Ostwald ripening must thus be suppressed to stabilize emulsions, e.g. to control the properties of pharmaceuticals, food, or cosmetics. Suppression of Ostwald ripening is also important in biological cells, which contain stable liquid-like compartments, e.g. germ granules, Cajal-bodies, and centrosomes. Such systems are often driven away from equilibrium by chemical reactions and can thus be called active emulsions. Here, we show that non-equilibrium chemical reactions can suppress Ostwald Ripening, leading to stable, monodisperse emulsions. We derive analytical approximations of the typical droplet size, droplet count, and time scale of the dynamics from a coarse-grained description of the droplet dynamics. We also compare these results to numerical simulations of the continuous concentration fields. Generally, we thus show how chemical reactions can be used to stabilize emulsions and to control their properties in technology and nature.

  12. Chemical reactions directed Peptide self-assembly.

    PubMed

    Rasale, Dnyaneshwar B; Das, Apurba K

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

  13. Chemical Reactions Directed Peptide Self-Assembly

    PubMed Central

    Rasale, Dnyaneshwar B.; Das, Apurba K.

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

  14. The smallest chemical reaction system with bistability

    PubMed Central

    Wilhelm, Thomas

    2009-01-01

    Background Bistability underlies basic biological phenomena, such as cell division, differentiation, cancer onset, and apoptosis. So far biologists identified two necessary conditions for bistability: positive feedback and ultrasensitivity. Results Biological systems are based upon elementary mono- and bimolecular chemical reactions. In order to definitely clarify all necessary conditions for bistability we here present the corresponding minimal system. According to our definition, it contains the minimal number of (i) reactants, (ii) reactions, and (iii) terms in the corresponding ordinary differential equations (decreasing importance from i-iii). The minimal bistable system contains two reactants and four irreversible reactions (three bimolecular, one monomolecular). We discuss the roles of the reactions with respect to the necessary conditions for bistability: two reactions comprise the positive feedback loop, a third reaction filters out small stimuli thus enabling a stable 'off' state, and the fourth reaction prevents explosions. We argue that prevention of explosion is a third general necessary condition for bistability, which is so far lacking discussion in the literature. Moreover, in addition to proving that in two-component systems three steady states are necessary for bistability (five for tristability, etc.), we also present a simple general method to design such systems: one just needs one production and three different degradation mechanisms (one production, five degradations for tristability, etc.). This helps modelling multistable systems and it is important for corresponding synthetic biology projects. Conclusion The presented minimal bistable system finally clarifies the often discussed question for the necessary conditions for bistability. The three necessary conditions are: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent explosions. This is important for modelling bistability with simple systems and for synthetically designing new bistable systems. Our simple model system is also well suited for corresponding teaching purposes. PMID:19737387

  15. Plasmon-driven sequential chemical reactions in an aqueous environment

    PubMed Central

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-01-01

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight. PMID:24958029

  16. Plasmon-driven sequential chemical reactions in an aqueous environment

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-06-01

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

  17. Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions

    ERIC Educational Resources Information Center

    Schultz, Emeric

    2008-01-01

    A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different

  18. Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions

    ERIC Educational Resources Information Center

    Schultz, Emeric

    2008-01-01

    A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

  19. 2005 Chemical Reactions at Surfaces

    SciTech Connect

    Cynthia M. Friend

    2006-03-14

    The Gordon Research Conference (GRC) on 2005 Chemical Reactions at Surfaces was held at Ventura Beach Marriott, Ventura California from February 13, 2005 through February 18, 2005. The Conference was well-attended with 124 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.

  20. Stochastic simulation of chemically activated unimolecular reactions

    NASA Astrophysics Data System (ADS)

    Vereecken, Luc; Huyberechts, Guido; Peeters, Jozef

    1997-04-01

    The kinetic master equation for the title processes can be formulated as a traditional deterministic set of coupled differential reaction-rate equations, or, alternatively, as a stochastic process in which each reaction is a random-walk transition in energy-species space. This stochastic description is the basis for three methods we describe here to numerically solve the kinetic master equation for chemically activated unimolecular reactions. The first method allows the calculation of the complete time evolution within a given mechanism, and is based on Gillespie's exact stochastic method (ESM). It is essentially a Monte Carlo simulation of the stochastic reaction processes. The second method allows for the direct calculation of the steady-state product distribution (DCPD). It describes the random walk within the framework of a discrete time Markov chain, and reduces the calculation of the steady-state product distribution to a fairly simple matrix algebra problem. The third method calculates the steady-state population of the intermediates (CSSPI), reformulating the solution of the master equation as an eigenvector problem generated by the description as a continuous time Markov chain. To our knowledge, the DCPD method has not been described before. Also, this is the first time that a CSSPI model is used explicitly in this type of calculation. The three methods are illustrated using the simple H+HNCO reaction, important in the RAPRENOx mechanism for NOx removal from flue gases.

  1. Microfabricated electrochemiluminescence cell for chemical reaction detection

    DOEpatents

    Northrup, M. Allen; Hsueh, Yun-Tai; Smith, Rosemary L.

    2003-01-01

    A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  2. Chemical reactions in low-g

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.; Facemire, B. R.

    1978-01-01

    The Apollo-Soyuz flight experiment, 'Chemical Foams' demonstrated that foams and air/liquid dispersions are much more stable in low-gravity than on the ground. It thus should be possible to conduct unique chemical reactions in space foams. The low-g results and subsequent ground work on the formaldehyde clock reaction indicate that the reaction is strongly influenced by (1) dissociated and undissociated solution species being adsorbed at solid/liquid and gas/liquid surfaces and (2) chemical reaction rates apparently being affected by long-range forces determined by the liquid mass and the extent and nature of all surface interfaces.

  3. 'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a greener chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation t...

  4. Microfabricated sleeve devices for chemical reactions

    DOEpatents

    Northrup, M. Allen (Berkeley, CA)

    2003-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  5. Modeling of turbulent chemical reaction

    NASA Technical Reports Server (NTRS)

    Chen, J.-Y.

    1995-01-01

    Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

  6. Kinetic studies of elementary chemical reactions

    SciTech Connect

    Durant, J.L. Jr.

    1993-12-01

    This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

  7. Entropy Generation in a Chemical Reaction

    ERIC Educational Resources Information Center

    Miranda, E. N.

    2010-01-01

    Entropy generation in a chemical reaction is analysed without using the general formalism of non-equilibrium thermodynamics at a level adequate for advanced undergraduates. In a first approach to the problem, the phenomenological kinetic equation of an elementary first-order reaction is used to show that entropy production is always positive. A

  8. Chemical Principles Revisited: Annotating Reaction Equations.

    ERIC Educational Resources Information Center

    Tykodi, R. J.

    1987-01-01

    Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

  9. Entropy Generation in a Chemical Reaction

    ERIC Educational Resources Information Center

    Miranda, E. N.

    2010-01-01

    Entropy generation in a chemical reaction is analysed without using the general formalism of non-equilibrium thermodynamics at a level adequate for advanced undergraduates. In a first approach to the problem, the phenomenological kinetic equation of an elementary first-order reaction is used to show that entropy production is always positive. A…

  10. Chemical reactions of organic compounds on clay surfaces.

    PubMed Central

    Soma, Y; Soma, M

    1989-01-01

    Chemical reactions of organic compounds including pesticides at the interlayer and exterior surfaces of clay minerals and with soil organic matter are reviewed. Representative reactions under moderate conditions possibly occurring in natural soils are described. Attempts have been made to clarify the importance of the chemical nature of molecules, their structures and their functional groups, and the Brnsted or Lewis acidity of clay minerals. PMID:2533556

  11. Importance of Reaction Mechanisms and Deformation on Gold Mineralisation

    NASA Astrophysics Data System (ADS)

    Pearce, M. A.; Hough, R.; Cleverley, J. S.

    2012-12-01

    Gold deposits are often associated with quartz and carbonate veining indicating mineralisation occurred during deformation and fluid flow. Investigation of several greenstone hosted deposits from Western Australia has shown that gold mineralisation in rocks that contain veins is often located in the wall rock not the veins themselves. This suggests that key processes are occurring in the wall rock causing the gold to precipitate from the fluid that carried it into the rocks. Continued reactions and deposition of gold demand that permeability is created and maintained in the host rocks. Microstructures are used to decipher the reactions that occurred in response to the gold-bearing fluid and to investigate the mechanisms of permeability generation in the host rocks. We present quantitative electron back-scatter diffraction data combined with spatially referenced major and trace-element chemistry to infer the reaction mechanisms active during fluid-rock interaction which potentially lead to the gold mineralisation. Data are presented showing the chemically driven recrystallisation of large (several mm) calcite grains to produce iron rich carbonates. Recystallisation occurs by nucleation of new grains which are in low energy orientations (epitactic and twin orientations) with respect to the host. The iron is sourced from large biotite and ilmenite grains which are breaking down as a result of the carbonate metasomatism to form fine grained polycrystalline aggregates. Biotite is reacting to muscovite and gold grains are found associated with this reaction (inter-mingled with the two micas and at the reaction fronts between them). In these samples, the importance of brittle deformation seems to be limited to vein creation allowing large volumes of fluid into the rock in the first place. There is evidence for limited crystal plastic deformation in the older carbonate and biotite grains. Reactions fronts in the biotite are perpendicular to the grain boundaries (as opposed to along the cleavage planes) so it is inferred that grain boundary fluid transport is more important than fracturing on the grain scale. Therefore, the grain-size reduction caused by the chemically induced recrystallisation is potentially of important in speeding up fluid transport through the rock. Gold depositions could be caused by a number of mechanisms including creation of space due to local volume loss during reactions or redox reactions that occur when iron is removed from ilmenite and biotite and incorporated into the carbonates.Biotite (pink) reacting to muscovite (red) and chlorite (green/blue) and associated gold mineralisation (black)

  12. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1990-01-01

    The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

  13. Fluid flow and chemical reaction kinetics in metamorphic systems

    SciTech Connect

    Lasaga, A.C.; Rye, D.M. )

    1993-05-01

    The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

  14. Chemical kinetic reaction mechanism for the combustion of propane

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.

    1984-01-01

    A detailed chemical kinetic reaction mechanism for the combustion of propane is presented and discussed. The mechanism consists of 27 chemical species and 83 elementary chemical reactions. Ignition and combustion data as determined in shock tube studies were used to evaluate the mechanism. Numerical simulation of the shock tube experiments showed that the kinetic behavior predicted by the mechanism for stoichiometric mixtures is in good agrement with the experimental results over the entire temperature range examined (1150-2600K). Sensitivity and theoretical studies carried out using the mechanism revealed that hydrocarbon reactions which are involved in the formation of the HO2 radical and the H2O2 molecule are very important in the mechanism and that the observed nonlinear behavior of ignition delay time with decreasing temperature can be interpreted in terms of the increased importance of the HO2 and H2O2 reactions at the lower temperatures.

  15. Quantum Chemical Approach to Estimating the Thermodynamics of Metabolic Reactions

    NASA Astrophysics Data System (ADS)

    Jinich, Adrian; Rappoport, Dmitrij; Dunn, Ian; Sanchez-Lengeling, Benjamin; Olivares-Amaya, Roberto; Noor, Elad; Even, Arren Bar; Aspuru-Guzik, Aln

    2014-11-01

    Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfer reactions and for reactions not including multiply charged anions. The errors in standard Gibbs reaction energy estimates are correlated with the charges of the participating molecules. The quantum chemical approach is amenable to systematic improvements and holds potential for providing thermodynamic data for all of metabolism.

  16. Quantum chemical approach to estimating the thermodynamics of metabolic reactions.

    PubMed

    Jinich, Adrian; Rappoport, Dmitrij; Dunn, Ian; Sanchez-Lengeling, Benjamin; Olivares-Amaya, Roberto; Noor, Elad; Even, Arren Bar; Aspuru-Guzik, Aln

    2014-01-01

    Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfer reactions and for reactions not including multiply charged anions. The errors in standard Gibbs reaction energy estimates are correlated with the charges of the participating molecules. The quantum chemical approach is amenable to systematic improvements and holds potential for providing thermodynamic data for all of metabolism. PMID:25387603

  17. Chemical reactions in liquid-phase microextraction.

    PubMed

    Xu, Li; Basheer, Chanbasha; Lee, Hian Kee

    2009-01-23

    In recent years, liquid-phase microextraction (LPME), a microscale implementation of liquid-liquid extraction, has become a very popular sample pretreatment technique because it combines extraction and enrichment, and is inexpensive, easy to operate and nearly solvent-free. Especially so in hollow fiber-protected LPME, sample cleanup is also effected. Essentially, owing to its high sample-to-extracting solvent volume ratio, LPME can achieve high analyte enrichment. Since its advent, the technique has been widely used, and applied to environmental, pharmaceutical, biological and forensic analyses. This review focuses on developments relating to chemical reactions associated with LPME applications, in contrast to conventional, straightforward extractions in which analytes remain as they are during the extraction process. Chemical reactions brought about during LPME serve to promote the extractability of the analytes (thus expanding the scope of applicability of the technique), facilitate their (analyte) compatibility with the analytical system and/or improve detection sensitivity. The reactions that are usually enabled during LPME include ion-pair extraction (carrier-mediated membrane transport), complexation, chemical (pre-extraction, in situ, and post-extraction) derivatization, phase-transfer catalysis and other "special affinity" reactions. Strategies on chemical reactions in LPME are overviewed in this report. PMID:18951550

  18. Aerosol simulation including chemical and nuclear reactions

    SciTech Connect

    Marwil, E.S.; Lemmon, E.C.

    1985-01-01

    The numerical simulation of aerosol transport, including the effects of chemical and nuclear reactions presents a challenging dynamic accounting problem. Particles of different sizes agglomerate and settle out due to various mechanisms, such as diffusion, diffusiophoresis, thermophoresis, gravitational settling, turbulent acceleration, and centrifugal acceleration. Particles also change size, due to the condensation and evaporation of materials on the particle. Heterogeneous chemical reactions occur at the interface between a particle and the suspending medium, or a surface and the gas in the aerosol. Homogeneous chemical reactions occur within the aersol suspending medium, within a particle, and on a surface. These reactions may include a phase change. Nuclear reactions occur in all locations. These spontaneous transmutations from one element form to another occur at greatly varying rates and may result in phase or chemical changes which complicate the accounting process. This paper presents an approach for inclusion of these effects on the transport of aerosols. The accounting system is very complex and results in a large set of stiff ordinary differential equations (ODEs). The techniques for numerical solution of these ODEs require special attention to achieve their solution in an efficient and affordable manner. 4 refs.

  19. Electronic energy density in chemical reaction systems

    NASA Astrophysics Data System (ADS)

    Tachibana, Akitomo

    2001-08-01

    The energy of chemical reaction is visualized in real space using the electronic energy density nE(r⃗) associated with the electron density n(r⃗). The electronic energy density nE(r⃗) is decomposed into the kinetic energy density nT(r⃗), the external potential energy density nV(r⃗), and the interelectron potential energy density nW(r⃗). Using the electronic energy density nE(r⃗) we can pick up any point in a chemical reaction system and find how the electronic energy E is assigned to the selected point. We can then integrate the electronic energy density nE(r⃗) in any region R surrounding the point and find out the regional electronic energy ER to the global E. The kinetic energy density nT(r⃗) is used to identify the intrinsic shape of the reactants, the electronic transition state, and the reaction products along the course of the chemical reaction coordinate. The intrinsic shape is identified with the electronic interface S that discriminates the region RD of the electronic drop from the region RA of the electronic atmosphere in the density distribution of the electron gas. If the R spans the whole space, then the integral gives the total E. The regional electronic energy ER in thermodynamic ensemble is realized in electrochemistry as the intrinsic Volta electric potential φR and the intrinsic Herring-Nichols work function ΦR. We have picked up first a hydrogen-like atom for which we have analytical exact expressions of the relativistic kinetic energy density nTM(r⃗) and its nonrelativistic version nT(r⃗). These expressions are valid for any excited bound states as well as the ground state. Second, we have selected the following five reaction systems and show the figures of the nT(r⃗) as well as the other energy densities along the intrinsic reaction coordinates: a protonation reaction to He, addition reactions of HF to C2H4 and C2H2, hydrogen abstraction reactions of NH3+ from HF and NH3. Valence electrons possess their unique delocalized drop region remote from those heavily localized drop regions adhered to core electrons. The kinetic energy density nT(r⃗) and the tension density τ⃗S(r⃗) can vividly demonstrate the formation of the chemical bond. Various basic chemical concepts in these chemical reaction systems have been clearly visualized in real three-dimensional space.

  20. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction

    NASA Astrophysics Data System (ADS)

    Wright, Stephen W.

    2002-01-01

    A color-change reaction is described in which two colorless solutions are combined to afford a black mixture. Two more colorless solutions are combined to afford a white mixture. The black and white mixtures are then combined to afford a clear, colorless solution. The reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, vinegar, ammonia, bleach, Epsom salt, and laundry starch.

  1. Classification of Chemical Reactions: Stages of Expertise

    ERIC Educational Resources Information Center

    Stains, Marilyne; Talanquer, Vicente

    2008-01-01

    In this study we explore the strategies that undergraduate and graduate chemistry students use when engaged in classification tasks involving symbolic and microscopic (particulate) representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention when classifying…

  2. Computer Animation of a Chemical Reaction.

    ERIC Educational Resources Information Center

    Eaker, Charles W.; Jacobs, Edwin L.

    1982-01-01

    Taking a prototype chemical reaction (molecular hydrogen plus hydrogen atom), constructs an accurate semiempirical, generalized diatomics-in-molecules potential energy surface, calculates motions of these atoms on this surface using REACTS trajectory program, and presents results as moving picture on a microcomputer graphics system. Provides

  3. Classification of Chemical Reactions: Stages of Expertise

    ERIC Educational Resources Information Center

    Stains, Marilyne; Talanquer, Vicente

    2008-01-01

    In this study we explore the strategies that undergraduate and graduate chemistry students use when engaged in classification tasks involving symbolic and microscopic (particulate) representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention when classifying

  4. Laboratory Studies of Heterogeneous Chemical Processes of Atmospheric Importance

    NASA Technical Reports Server (NTRS)

    Molina, Mario J.

    2004-01-01

    The objective of this study is to conduct measurements of chemical kinetics parameters for heterogeneous reactions of importance in the stratosphere and the troposphere. It involves the elucidation of the mechanism of the interaction of HCl vapor with ice surfaces, which is the first step in the heterogeneous chlorine activation processes, as well as the investigation of the atmospheric oxidation mechanism of soot particles emitted by biomass and fossil fuels. The techniques being employed include turbulent flow-chemical ionization mass spectrometry and optical ellipsometry, among others.

  5. Chemical reactions in reverse micelle systems

    DOEpatents

    Matson, Dean W.; Fulton, John L.; Smith, Richard D.; Consani, Keith A.

    1993-08-24

    This invention is directed to conducting chemical reactions in reverse micelle or microemulsion systems comprising a substantially discontinuous phase including a polar fluid, typically an aqueous fluid, and a microemulsion promoter, typically a surfactant, for facilitating the formation of reverse micelles in the system. The system further includes a substantially continuous phase including a non-polar or low-polarity fluid material which is a gas under standard temperature and pressure and has a critical density, and which is generally a water-insoluble fluid in a near critical or supercritical state. Thus, the microemulsion system is maintained at a pressure and temperature such that the density of the non-polar or low-polarity fluid exceeds the critical density thereof. The method of carrying out chemical reactions generally comprises forming a first reverse micelle system including an aqueous fluid including reverse micelles in a water-insoluble fluid in the supercritical state. Then, a first reactant is introduced into the first reverse micelle system, and a chemical reaction is carried out with the first reactant to form a reaction product. In general, the first reactant can be incorporated into, and the product formed in, the reverse micelles. A second reactant can also be incorporated in the first reverse micelle system which is capable of reacting with the first reactant to form a product.

  6. Concordant Chemical Reaction Networks and the Species-Reaction Graph

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    In a recent paper it was shown that, for chemical reaction networks possessing a subtle structural property called concordance, dynamical behavior of a very circumscribed (and largely stable) kind is enforced, so long as the kinetics lies within the very broad and natural weakly monotonic class. In particular, multiple equilibria are precluded, as are degenerate positive equilibria. Moreover, under certain circumstances, also related to concordance, all real eigenvalues associated with a positive equilibrium are negative. Although concordance of a reaction network can be decided by readily available computational means, we show here that, when a nondegenerate network’s Species-Reaction Graph satisfies certain mild conditions, concordance and its dynamical consequences are ensured. These conditions are weaker than earlier ones invoked to establish kinetic system injectivity, which, in turn, is just one ramification of network concordance. Because the Species-Reaction Graph resembles pathway depictions often drawn by biochemists, results here expand the possibility of inferring significant dynamical information directly from standard biochemical reaction diagrams. PMID:22940368

  7. ReactionPredictor: prediction of complex chemical reactions at the mechanistic level using machine learning.

    PubMed

    Kayala, Matthew A; Baldi, Pierre

    2012-10-22

    Proposing reasonable mechanisms and predicting the course of chemical reactions is important to the practice of organic chemistry. Approaches to reaction prediction have historically used obfuscating representations and manually encoded patterns or rules. Here we present ReactionPredictor, a machine learning approach to reaction prediction that models elementary, mechanistic reactions as interactions between approximate molecular orbitals (MOs). A training data set of productive reactions known to occur at reasonable rates and yields and verified by inclusion in the literature or textbooks is derived from an existing rule-based system and expanded upon with manual curation from graduate level textbooks. Using this training data set of complex polar, hypervalent, radical, and pericyclic reactions, a two-stage machine learning prediction framework is trained and validated. In the first stage, filtering models trained at the level of individual MOs are used to reduce the space of possible reactions to consider. In the second stage, ranking models over the filtered space of possible reactions are used to order the reactions such that the productive reactions are the top ranked. The resulting model, ReactionPredictor, perfectly ranks polar reactions 78.1% of the time and recovers all productive reactions 95.7% of the time when allowing for small numbers of errors. Pericyclic and radical reactions are perfectly ranked 85.8% and 77.0% of the time, respectively, rising to >93% recovery for both reaction types with a small number of allowed errors. Decisions about which of the polar, pericyclic, or radical reaction type ranking models to use can be made with >99% accuracy. Finally, for multistep reaction pathways, we implement the first mechanistic pathway predictor using constrained tree-search to discover a set of reasonable mechanistic steps from given reactants to given products. Webserver implementations of both the single step and pathway versions of ReactionPredictor are available via the chemoinformatics portal http://cdb.ics.uci.edu/. PMID:22978639

  8. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A new global potential energy surface (PES) is being generated for O(P-3) + H2 yields OH + H. This surface is being fit using the rotated Morse oscillator method, which was used to fit the previous POL-CI surface. The new surface is expected to be more accurate and also includes a much more complete sampling of bent geometries. A new study has been undertaken of the reaction N + O2 yields NO + O. The new studies have focused on the region of the surface near a possible minimum corresponding to the peroxy form of NOO. A large portion of the PES for this second reaction has been mapped out. Since state to state cross sections for the reaction are important in the chemistry of high temperature air, these studies will probably be extended to permit generation of a new global potential for reaction.

  9. Researches on Preliminary Chemical Reactions in Spark-Ignition Engines

    NASA Technical Reports Server (NTRS)

    Muehlner, E.

    1943-01-01

    Chemical reactions can demonstrably occur in a fuel-air mixture compressed in the working cylinder of an Otto-cycle (spark ignition) internal-combustion engine even before the charge is ignited by the flame proceeding from the sparking plug. These are the so-called "prelinminary reactions" ("pre-flame" combustion or oxidation), and an exact knowledge of their characteristic development is of great importance for a correct appreciation of the phenomena of engine-knock (detonation), and consequently for its avoidance. Such reactions can be studied either in a working engine cylinder or in a combustion bomb. The first method necessitates a complicated experimental technique, while the second has the disadvantage of enabling only a single reaction to be studied at one time. Consequently, a new series of experiments was inaugurated, conducted in a motored (externally-driven) experimental engine of mixture-compression type, without ignition, the resulting preliminary reactions being detectable and measurable thermometrically.

  10. Quantum mechanics of chemical reactions: Recent developments in reactive scattering and in reaction path Hamiltonians

    SciTech Connect

    Miller, W.H.

    1988-12-01

    Two recent developments in the theory of chemical reaction dynamics are reviewed. First, it has recently been discovered that the S- matrix version of the Kohn variational principle is free of the ''Kohn anomalies'' that have plagued other versions and prevented its general use. This has considerably simplified quantum mechanical reactive scattering calculations, which provide the rigorous characterizations of bimolecular reactions. Second, a new kind of reaction path Hamiltonian has been developed, one based on the ''least motion'' path that interpolates linearly between the reactant and product geometry of the molecule (rather than the previously used minimum energy, or ''intrinsic'' reaction path). The form of Hamiltonian which results is much simpler than the original reaction path Hamiltonian, but more important is the fact that it provides a more physically correct description of hydrogen atom transfer reactions. 44 refs., 4 figs.

  11. Quantum dynamics of fast chemical reactions

    SciTech Connect

    Light, J.C.

    1993-12-01

    The aims of this research are to explore, develop, and apply theoretical methods for the evaluation of the dynamics of gas phase collision processes, primarily chemical reactions. The primary theoretical tools developed for this work have been quantum scattering theory, both in time dependent and time independent forms. Over the past several years, the authors have developed and applied methods for the direct quantum evaluation of thermal rate constants, applying these to the evaluation of the hydrogen isotopic exchange reactions, applied wave packet propagation techniques to the dissociation of Rydberg H{sub 3}, incorporated optical potentials into the evaluation of thermal rate constants, evaluated the use of optical potentials for state-to-state reaction probability evaluations, and, most recently, have developed quantum approaches for electronically non-adiabatic reactions which may be applied to simplify calculations of reactive, but electronically adiabatic systems. Evaluation of the thermal rate constants and the dissociation of H{sub 3} were reported last year, and have now been published.

  12. Chemical Looping Combustion Reactions and Systems

    SciTech Connect

    Sarofim, Adel; Lighty, JoAnn; Smith, Philip; Whitty, Kevin; Eyring, Edward; Sahir, Asad; Alvarez, Milo; Hradisky, Michael; Clayton, Chris; Konya, Gabor; Baracki, Richard; Kelly, Kerry

    2014-03-01

    Chemical Looping Combustion (CLC) is one promising fuel-combustion technology, which can facilitate economic CO{sub 2} capture in coal-fired power plants. It employs the oxidation/reduction characteristics of a metal, or oxygen carrier, and its oxide, the oxidizing gas (typically air) and the fuel source may be kept separate. This topical report discusses the results of four complementary efforts: (5.1) the development of process and economic models to optimize important design considerations, such as oxygen carrier circulation rate, temperature, residence time; (5.2) the development of high-performance simulation capabilities for fluidized beds and the collection, parameter identification, and preliminary verification/uncertainty quantification; (5.3) the exploration of operating characteristics in the laboratoryscale bubbling bed reactor, with a focus on the oxygen carrier performance, including reactivity, oxygen carrying capacity, attrition resistance, resistance to deactivation, cost and availability; and (5.4) the identification of kinetic data for copper-based oxygen carriers as well as the development and analysis of supported copper oxygen carrier material. Subtask 5.1 focused on the development of kinetic expressions for the Chemical Looping with Oxygen Uncoupling (CLOU) process and validating them with reported literature data. The kinetic expressions were incorporated into a process model for determination of reactor size and oxygen carrier circulation for the CLOU process using ASPEN PLUS. An ASPEN PLUS process model was also developed using literature data for the CLC process employing an iron-based oxygen carrier, and the results of the process model have been utilized to perform a relative economic comparison. In Subtask 5.2, the investigators studied the trade-off between modeling approaches and available simulations tools. They quantified uncertainty in the high-performance computing (HPC) simulation tools for CLC bed applications. Furthermore, they performed a sensitivity analysis for velocity, height and polydispersity and compared results against literature data for experimental studies of CLC beds with no reaction. Finally, they present an optimization space using simple non-reactive configurations. In Subtask 5.3, through a series of experimental studies, behavior of a variety of oxygen carriers with different loadings and manufacturing techniques was evaluated under both oxidizing and reducing conditions. The influences of temperature, degree of carrier conversion and thermodynamic driving force resulting from the difference between equilibrium and system O{sub 2} partial pressures were evaluated through several experimental campaigns, and generalized models accounting for these influences were developed to describe oxidation and oxygen release. Conversion of three solid fuels with widely ranging reactivities was studied in a small fluidized bed system, and all but the least reactive fuel (petcoke) were rapidly converted by oxygen liberated from the CLOU carrier. Attrition propensity of a variety of carriers was also studied, and the carriers produced by freeze granulation or impregnation of preformed substrates displayed the lowest rates of attrition. Subtask 5.4 focused on gathering kinetic data for a copper-based oxygen carrier to assist with modeling of a functioning chemical looping reactor. The kinetics team was also responsible for the development and analysis of supported copper oxygen carrier material.

  13. Chemical Reactions in Hexagonal Boron Nitride System

    NASA Astrophysics Data System (ADS)

    Hubáček, Milan; Ueki, Masanori

    1996-05-01

    Chemical reactions of synthesis of hexagonal boron nitride and their mechanisms are discussed and classified. Based on their analyses, a ternary B-N-O diagram is suggested, in which virtual compositions of hexagonal boron nitride ceramic and preceding materials, starting with a mixture of raw materials, through oligomolecular semi-organic precursors and turbostratic boron nitride powder are specified. Beside the composition, processes of conversion between particular substances, such as synthesis, decomposition and crystallization of boron nitride powder, and sintering and hydrolysis of ceramic, are characterized by vectors—elements of the ternary diagram. The dynamic model is suggested to be generally applied to systems with prevailingly covalent character, where the polymerization is regarded as a controlling chemical process.

  14. Multiscale stochastic simulations of chemical reactions with regulated scale separation

    SciTech Connect

    Koumoutsakos, Petros; Feigelman, Justin

    2013-07-01

    We present a coupling of multiscale frameworks with accelerated stochastic simulation algorithms for systems of chemical reactions with disparate propensities. The algorithms regulate the propensities of the fast and slow reactions of the system, using alternating micro and macro sub-steps simulated with accelerated algorithms such as τ and R-leaping. The proposed algorithms are shown to provide significant speedups in simulations of stiff systems of chemical reactions with a trade-off in accuracy as controlled by a regulating parameter. More importantly, the error of the methods exhibits a cutoff phenomenon that allows for optimal parameter choices. Numerical experiments demonstrate that hybrid algorithms involving accelerated stochastic simulations can be, in certain cases, more accurate while faster, than their corresponding stochastic simulation algorithm counterparts.

  15. The role of chemical reactions in the Chernobyl accident

    NASA Astrophysics Data System (ADS)

    Grishanin, E. I.

    2010-12-01

    It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80-110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.

  16. The role of chemical reactions in the Chernobyl accident

    SciTech Connect

    Grishanin, E. I.

    2010-12-15

    It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80-110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000 Degree-Sign C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.

  17. Molecular Dynamics Simulations of Chemical Reactions for Use in Education

    ERIC Educational Resources Information Center

    Qian Xie; Tinker, Robert

    2006-01-01

    One of the simulation engines of an open-source program called the Molecular Workbench, which can simulate thermodynamics of chemical reactions, is described. This type of real-time, interactive simulation and visualization of chemical reactions at the atomic scale could help students understand the connections between chemical reaction equations…

  18. Molecular Dynamics Simulations of Chemical Reactions for Use in Education

    ERIC Educational Resources Information Center

    Qian Xie; Tinker, Robert

    2006-01-01

    One of the simulation engines of an open-source program called the Molecular Workbench, which can simulate thermodynamics of chemical reactions, is described. This type of real-time, interactive simulation and visualization of chemical reactions at the atomic scale could help students understand the connections between chemical reaction equations

  19. Computed Potential Energy Surfaces for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A manuscript describing the calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction, which were described in the last progress report, has been accepted for publication in J. Chem. Phys., and a copy of the manuscript is included in the appendix. The production of (1)CH2 in this reaction is important in hydrocarbon combustion since (1)CH2 is highly reactive and would be expected to insert into N2, possibly leading to a new source for prompt NO(x) (vide infra). During the last six months new calculations have been carried out for the NH2 + NO system, which is important in the thermal de-NO(x) process.

  20. Laboratory Studies of Heterogeneous Chemical Processes of Atmospheric Importance

    NASA Technical Reports Server (NTRS)

    Molina, Mario J.

    2003-01-01

    The objective of this study is to conduct measurements of chemical kinetics parameters for heterogeneous reactions of importance in the stratosphere and the troposphere. It involves the elucidation of the mechanism of the interaction of HC1 vapor with ice surfaces, which is the first step in the heterogeneous chlorine activation processes, as well as the investigation of the atmospheric oxidation mechanism of soot particles emitted by biomass and fossil fuels. The techniques being employed include turbulent flow- chemical ionization mass spectrometry and optical ellipsometry, among others. The next section summarizes our research activities during the first year of the project, and the section that follows consists of the statement of work for the second year.

  1. Mapping students' ideas about chemical reactions at different educational levels

    NASA Astrophysics Data System (ADS)

    Yan, Fan

    Understanding chemical reactions is crucial in learning chemistry at all educational levels. Nevertheless, research in science education has revealed that many students struggle to understand chemical processes. Improving teaching and learning about chemical reactions demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the discipline. Thus, we have carried out a qualitative study using semi-structured interviews as the main data collection tool to explore students reasoning about reaction mechanism and causality. The participants of this study included students at different levels of training in chemistry: general chemistry students (n=22), organic chemistry students (n=16), first year graduate students (n=13) and Ph.D. candidates (n=14). We identified major conceptual modes along critical dimensions of analysis, and illustrated common ways of reasoning using typical cases. Main findings indicate that although significant progress is observed in student reasoning in some areas, major conceptual difficulties seem to persist even at the more advanced educational levels. In addition, our findings suggest that students struggle to integrate important concepts when thinking about mechanism and causality in chemical reactions. The results of our study are relevant to chemistry educators interested in learning progressions, assessment, and conceptual development.

  2. DSMC Predictions of Chemical Reaction Rates between Atmospheric Species

    NASA Astrophysics Data System (ADS)

    Gallis, M. A.; Bond, R. B.; Torczynski, J. R.

    2009-11-01

    A recently proposed chemical reaction model based solely on molecular-level information is applied to calculate equilibrium and non-equilibrium chemical reaction rates for atmospheric reactions in hypersonic flows. The DSMC model is capable of reproducing measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular-level properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. The DSMC-predicted chemical reaction rates are compared to theoretically calculated and experimentally measured reaction rates for non-equilibrium conditions. The observed agreement provides strong evidence that molecular-level modeling of chemical reactions provides an accurate method for predicting equilibrium and non-equilibrium chemical reaction rates. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  3. Quantum theory of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1994-10-01

    If one wishes to describe a chemical reaction at the most detailed level possible, i.e., its state-to-state differential scattering cross section, then it is necessary to solve the Schroedinger equation to obtain the S-matrix as a function of total energy E and total angular momentum J, in terms of which the cross sections can be calculated as given by equation (1) in the paper. All other physically observable attributes of the reaction can be derived from the cross sections. Often, in fact, one is primarily interested in the least detailed quantity which characterizes the reaction, namely its thermal rate constant, which is obtained by integrating Eq. (1) over all scattering angles, summing over all product quantum states, and Boltzmann-averaging over all initial quantum states of reactants. With the proper weighting factors, all of these averages are conveniently contained in the cumulative reaction probability (CRP), which is defined by equation (2) and in terms of which the thermal rate constant is given by equation (3). Thus, having carried out a full state-to-state scattering calculation to obtain the S-matrix, one can obtain the CRP from Eq. (2), and then rate constant from Eq. (3), but this seems like ``overkill``; i.e., if one only wants the rate constant, it would clearly be desirable to have a theory that allows one to calculate it, or the CRP, more directly than via Eq. (2), yet also correctly, i.e., without inherent approximations. Such a theory is the subject of this paper.

  4. Chemical attenuation reactions of selenium; Final report

    SciTech Connect

    Zachara, J.M.; Rai, D.; Moore, D.A.; Turner, G.D.; Felmy, A.R.

    1994-02-01

    This report summarizes research on the geochemical behavior of Se present in utility coal-combustion wastes. Laboratory experiments quantified select geochemical reactions that control the concentrations of selenite (SeO{sub 3}{sup 2{minus}}) and selenate (SeO{sub 4}{sup 2{minus}}) in soil solutions and groundwater and determined the magnitude and mechanisms of chemical attenuation of these species in soils and subsurface materials. Thermodynamic data, equilibrium constants, and modeling procedures were developed that to utilities to make improved predictions of the mobility of Se species from ponded and dry landfill sites. An adsorption-constant database for selenite and selenate on common soil minerals was developed. The database, which can be used to estimate the extent of Se attenuation by adsorption in utility soils, was used to determine the specific mineral phases control the adsorption of selenite (Fe oxides) and selenate (Al oxides). Solubility studies were performed with two Se solid phases that may form in the environment [BaSeO{sub 4}(c) and Fe{sub 2}(SeO{sub 3}){sub 3}{lg_bullet}6H{sub 2}0(c)] to establish upper limits on Se concentrations. New thermodynamic data were developed to allow prediction of aqueous Se concentrations where these phases may exist. Eleven soil and subsurface materials, collected nationally and representative of properties frequently encountered at waste sites, were used in experiments involving adsorption of selenite and selenate to assess their potential for Se chemical attenuation and to determine chemical and mineralogic factors that control Se adsorption. Selenite was far more strongly adsorbed by the geologic materials than the selenate. The adsorption of both Se species depended on the type of natural materials and showed positive correlation with Fe and Al oxides associated with particle surfaces. Procedures were developed to predict Se adsorption from comprehensive chemical and mineralogic characterization data.

  5. Thermodynamic performance for a chemical reactions model

    NASA Astrophysics Data System (ADS)

    Gonzalez-Narvaez, R. E.; Sánchez-Salas, N.; Chimal-Eguía, J. C.

    2015-01-01

    This paper presents the analysis efficiency of a chemical reaction model of four states, such that their activated states can occur at any point (fixed but arbitrary) of the transition from one state to another. This mechanism operates under a single heat reservoir temperature, unlike the internal combustion engines where there are two thermal sources. Different efficiencies are compared to this model, which operate at different optimum engine regimes. Thus, some analytical methods are used to give an approximate expression, facilitating the comparison between them. Finally, the result is compared with that obtained by other authors considered a general model of an isothermal molecular machine. Taking into account the above, the results seems to follow a similar behaviour for all the optimized engines, which resemble that observed in the case of heat engine efficiencies.

  6. Assessing the importance of proton transfer reactions in DNA.

    PubMed

    Jacquemin, Denis; Ziga, Jos; Requena, Alberto; Cron-Carrasco, Jos Pedro

    2014-08-19

    Although engineered by millions of years of evolution, the cellular machinery is not flawless, and errors regularly appear during DNA replication. The subsequent alteration of the stored genetic message results in a mutation and might be the starting point of important health disorders. The question therefore is what causes DNA mutations? All living organisms are constantly exposed to a number of external agents such as free radicals and to radiation, which may lead to induced mutations. There are also mutations happening without invoking the action of any exogenous element, the so-called spontaneous mutations. The former can be partially controlled by avoiding exposure to high-risk environments, while the latter are more intriguing because their origin is unclear and difficult to determine. As noted by Watson and Crick when they first discovered the DNA structure, the correct replication of DNA rests on the assumption that the base pairs remain in their most stable, canonical form. However, protons along the interbase hydrogen-bond network are not static entities. They can in fact interchange their positions in DNA bases through proton transfer (PT) reactions before strands unwind, giving rise to noncanonical structures defined as rare tautomers. The importance of these rare tautomers was also cleverly anticipated by Watson and Crick and some years later claimed by Lwdin to be a source of spontaneous mutations. In Watson and Crick's words: "It would be of interest to know the precise difference in free energy between the various tautomeric forms under physiological conditions." Unfortunately, rare tautomeric forms are very difficult to detect, so no direct and accurate free energy measure has been discerned. In contrast, theoretical chemistry is making good progress toward the quantification of PT reactions in DNA and their biological consequences. This Account touches upon the theoretical studies devoted to appraising the importance of rare tautomers as promoters of spontaneous mutations. We focus in particular on the crucial role played by the biological environment on DNA stability. It has now been demonstrated that valuable macroscopic predictions require not only highly accurate theories but also refined chemical models. Hybrid quantum mechanics/molecular mechanics (QM/MM) simulations performed on short but complete DNA sequence fragments emerge in this context as the most adequate tools. In addition, these methods can be used to quantify the effect of different external agents on the PT tautomeric equilibria and, eventually, to conveniently handle them. This is the case for the possible alteration of the naturally observed mutation rate by exposure to intense electric fields. Theoretical predictions envision in this respect promising applications of ultrashort electric pulses in medicine to selectively modify the mutated/canonical ratio in DNA. PMID:24849375

  7. Cellular Metabolic Network Analysis: Discovering Important Reactions in Treponema pallidum

    PubMed Central

    Chen, Xueying; Zhao, Min; Qu, Hong

    2015-01-01

    T. pallidum, the syphilis-causing pathogen, performs very differently in metabolism compared with other bacterial pathogens. The desire for safe and effective vaccine of syphilis requests identification of important steps in T. pallidum's metabolism. Here, we apply Flux Balance Analysis to represent the reactions quantitatively. Thus, it is possible to cluster all reactions in T. pallidum. By calculating minimal cut sets and analyzing topological structure for the metabolic network of T. pallidum, critical reactions are identified. As a comparison, we also apply the analytical approaches to the metabolic network of H. pylori to find coregulated drug targets and unique drug targets for different microorganisms. Based on the clustering results, all reactions are further classified into various roles. Therefore, the general picture of their metabolic network is obtained and two types of reactions, both of which are involved in nucleic acid metabolism, are found to be essential for T. pallidum. It is also discovered that both hubs of reactions and the isolated reactions in purine and pyrimidine metabolisms play important roles in T. pallidum. These reactions could be potential drug targets for treating syphilis. PMID:26495292

  8. Silicon-based sleeve devices for chemical reactions

    DOEpatents

    Northrup, M.A.; Mariella, R.P. Jr.; Carrano, A.V.; Balch, J.W.

    1996-12-31

    A silicon-based sleeve type chemical reaction chamber is described that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis. 32 figs.

  9. Silicon-based sleeve devices for chemical reactions

    DOEpatents

    Northrup, M. Allen (Berkeley, CA); Mariella, Jr., Raymond P. (Danville, CA); Carrano, Anthony V. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

    1996-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  10. Chemical reaction fouling model for single-phase heat transfer

    SciTech Connect

    Panchal, C.B.; Watkinson, A.P.

    1993-08-01

    A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differ for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.

  11. A chemical reaction network solver for the astrophysics code NIRVANA

    NASA Astrophysics Data System (ADS)

    Ziegler, U.

    2016-02-01

    Context. Chemistry often plays an important role in astrophysical gases. It regulates thermal properties by changing species abundances and via ionization processes. This way, time-dependent cooling mechanisms and other chemistry-related energy sources can have a profound influence on the dynamical evolution of an astrophysical system. Modeling those effects with the underlying chemical kinetics in realistic magneto-gasdynamical simulations provide the basis for a better link to observations. Aims: The present work describes the implementation of a chemical reaction network solver into the magneto-gasdynamical code NIRVANA. For this purpose a multispecies structure is installed, and a new module for evolving the rate equations of chemical kinetics is developed and coupled to the dynamical part of the code. A small chemical network for a hydrogen-helium plasma was constructed including associated thermal processes which is used in test problems. Methods: Evolving a chemical network within time-dependent simulations requires the additional solution of a set of coupled advection-reaction equations for species and gas temperature. Second-order Strang-splitting is used to separate the advection part from the reaction part. The ordinary differential equation (ODE) system representing the reaction part is solved with a fourth-order generalized Runge-Kutta method applicable for stiff systems inherent to astrochemistry. Results: A series of tests was performed in order to check the correctness of numerical and technical implementation. Tests include well-known stiff ODE problems from the mathematical literature in order to confirm accuracy properties of the solver used as well as problems combining gasdynamics and chemistry. Overall, very satisfactory results are achieved. Conclusions: The NIRVANA code is now ready to handle astrochemical processes in time-dependent simulations. An easy-to-use interface allows implementation of complex networks including thermal processes. In combination with NIRVANA's self-gravity solver, its efficient solver for dissipation terms and its adaptive mesh refinement capability challenging astrophysical problems come into reach with the code.

  12. CHEMICALS INCORPORATED IN NEST MATERIAL BY RED IMPORTED FIRE ANTS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Red imported fire ants are believed to incorporate ant-derived chemicals in nesting material. However, only a few chemicals have been identified. One hurdle for such investigation is the interference in chemical analysis from soil-borne chemicals. Ants were found to be able to construct their nes...

  13. Detailed Chemical Kinetic Reaction Mechanism for Biodiesel Components Methyl Stearate and Methyl Oleate

    SciTech Connect

    Naik, C; Westbrook, C K; Herbinet, O; Pitz, W J; Mehl, M

    2010-01-22

    New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel/air autoignition delay times and comparing the results with more conventional hydrocarbon fuels for which experimental results are available. Additional comparisons were carried out with measured results taken from jet-stirred reactor experiments for rapeseed methyl ester fuels. In both sets of computational tests, methyl oleate was found to be slightly less reactive than methyl stearate, and an explanation of this observation is made showing that the double bond in methyl oleate inhibits certain low temperature chain branching reaction pathways important in methyl stearate. The resulting detailed chemical kinetic reaction mechanism includes more approximately 3500 chemical species and more than 17,000 chemical reactions.

  14. 40 CFR 799.19 - Chemical imports and exports.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... the requirements of 40 CFR part 707. ... 40 Protection of Environment 32 2011-07-01 2011-07-01 false Chemical imports and exports. 799.19... CONTROL ACT (CONTINUED) IDENTIFICATION OF SPECIFIC CHEMICAL SUBSTANCE AND MIXTURE TESTING...

  15. 40 CFR 799.19 - Chemical imports and exports.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... the requirements of 40 CFR part 707. ... 40 Protection of Environment 31 2010-07-01 2010-07-01 true Chemical imports and exports. 799.19... CONTROL ACT (CONTINUED) IDENTIFICATION OF SPECIFIC CHEMICAL SUBSTANCE AND MIXTURE TESTING...

  16. 40 CFR 799.19 - Chemical imports and exports.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... the requirements of 40 CFR part 707. ... 40 Protection of Environment 33 2012-07-01 2012-07-01 false Chemical imports and exports. 799.19... CONTROL ACT (CONTINUED) IDENTIFICATION OF SPECIFIC CHEMICAL SUBSTANCE AND MIXTURE TESTING...

  17. 40 CFR 799.19 - Chemical imports and exports.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... the requirements of 40 CFR part 707. ... 40 Protection of Environment 33 2013-07-01 2013-07-01 false Chemical imports and exports. 799.19... CONTROL ACT (CONTINUED) IDENTIFICATION OF SPECIFIC CHEMICAL SUBSTANCE AND MIXTURE TESTING...

  18. 40 CFR 799.19 - Chemical imports and exports.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... the requirements of 40 CFR part 707. ... 40 Protection of Environment 32 2014-07-01 2014-07-01 false Chemical imports and exports. 799.19... CONTROL ACT (CONTINUED) IDENTIFICATION OF SPECIFIC CHEMICAL SUBSTANCE AND MIXTURE TESTING...

  19. Heterogeneous chemical reactions: Preparation of monodisperse latexes

    NASA Technical Reports Server (NTRS)

    Vanderhoff, J. W.; Micale, F. J.; El-Aasser, M. S.; Sterk, A. A.; Bethke, G. W.

    1977-01-01

    It is demonstrated that a photoinitiated emulsion polymerization can be carried out to a significant conversion in a SPAR rocket prototype polymerization vessel within the six minutes allowed for the experiment. The percentage of conversion was determined by both dilatometry and gravimetric methods with good agreement. The experimental results lead to the following conclusions: (1) emulsion polymerizations can be carried out to conversions as high as 75%, using a stable micellized styrene-SLS system plus photoinitiator; (2) dilatometry can be used to accurately determine both the rate and conversion of polymerization; (3) thermal expansion due to the light source and heat of reaction is small and can be corrected for if necessary; (4) although seeded emulsion polymerizations are unfavorable in photoinitiation, as opposed to chemical initiation, polymerizations can be carried out to at least 15% conversion using 7940A seed particles, with 0.05% solids; and (5) photoinitiation should be used to initiate polymerization in the SPAR rocket experiments because of the mechanical simplicity of the experiment.

  20. Prediction and Prevention of Chemical Reaction Hazards: Learning by Simulation.

    ERIC Educational Resources Information Center

    Shacham, Mordechai; Brauner, Neima; Cutlip, Michael B.

    2001-01-01

    Points out that chemical hazards are the major cause of accidents in chemical industry and describes a safety teaching approach using a simulation. Explains a problem statement on exothermic liquid-phase reactions. (YDS)

  1. GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Green chemical synthesis through catalysis and alternate reaction conditions

    Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

  2. Crossed molecular beam studies of atmospheric chemical reaction dynamics

    SciTech Connect

    Zhang, Jingsong

    1993-04-01

    The dynamics of several elementary chemical reactions that are important in atmospheric chemistry are investigated. The reactive scattering of ground state chlorine or bromine atoms with ozone molecules and ground state chlorine atoms with nitrogen dioxide molecules is studied using a crossed molecular beams apparatus with a rotatable mass spectrometer detector. The Cl + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at four collision energies ranging from 6 kcal/mole to 32 kcal/mole. The derived product center-of-mass angular and translational energy distributions show that the reaction has a direct reaction mechanism and that there is a strong repulsion on the exit channel. The ClO product is sideways and forward scattered with respect to the Cl atom, and the translational energy release is large. The Cl atom is most likely to attack the terminal oxygen atom of the ozone molecule. The Br + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at five collision energies ranging from 5 kcal/mole to 26 kcal/mole. The derived product center-of-mass angular and translational energy distributions are quite similar to those in the Cl + O{sub 3} reaction. The Br + O{sub 3} reaction has a direct reaction mechanism similar to that of the Cl + O{sub 3} reaction. The electronic structure of the ozone molecule seems to play the central role in determining the reaction mechanism in atomic radical reactions with the ozone molecule. The Cl + NO{sub 2} {yields} ClO + NO reaction has been studied at three collision energies ranging from 10.6 kcal/mole to 22.4 kcal/mole. The center-of-mass angular distribution has some forward-backward symmetry, and the product translational energy release is quite large. The reaction proceeds through a short-lived complex whose lifetime is less than one rotational period. The experimental results seem to show that the Cl atom mainly attacks the oxygen atom instead of the nitrogen atom of the NO{sub 2} molecule.

  3. Incidents of chemical reactions in cell equipment

    SciTech Connect

    Baldwin, N.M.; Barlow, C.R.

    1991-12-31

    Strongly exothermic reactions can occur between equipment structural components and process gases under certain accident conditions in the diffusion enrichment cascades. This paper describes the conditions required for initiation of these reactions, and describes the range of such reactions experienced over nearly 50 years of equipment operation in the US uranium enrichment program. Factors are cited which can promote or limit the destructive extent of these reactions, and process operations are described which are designed to control the reactions to minimize equipment damage, downtime, and the possibility of material releases.

  4. Deterministic Function Computation with Chemical Reaction Networks*

    PubMed Central

    Chen, Ho-Lin; Doty, David; Soloveichik, David

    2013-01-01

    Chemical reaction networks (CRNs) formally model chemistry in a well-mixed solution. CRNs are widely used to describe information processing occurring in natural cellular regulatory networks, and with upcoming advances in synthetic biology, CRNs are a promising language for the design of artificial molecular control circuitry. Nonetheless, despite the widespread use of CRNs in the natural sciences, the range of computational behaviors exhibited by CRNs is not well understood. CRNs have been shown to be efficiently Turing-universal (i.e., able to simulate arbitrary algorithms) when allowing for a small probability of error. CRNs that are guaranteed to converge on a correct answer, on the other hand, have been shown to decide only the semilinear predicates (a multi-dimensional generalization of “eventually periodic” sets). We introduce the notion of function, rather than predicate, computation by representing the output of a function f : ℕk → ℕl by a count of some molecular species, i.e., if the CRN starts with x1, …, xk molecules of some “input” species X1, …, Xk, the CRN is guaranteed to converge to having f(x1, …, xk) molecules of the “output” species Y1, …, Yl. We show that a function f : ℕk → ℕl is deterministically computed by a CRN if and only if its graph {(x, y) ∈ ℕk × ℕl ∣ f(x) = y} is a semilinear set. Finally, we show that each semilinear function f (a function whose graph is a semilinear set) can be computed by a CRN on input x in expected time O(polylog ∥x∥1). PMID:25383068

  5. Semiclassical methods in chemical reaction dynamics

    SciTech Connect

    Keshavamurthy, S.

    1994-12-01

    Semiclassical approximations, simple as well as rigorous, are formulated in order to be able to describe gas phase chemical reactions in large systems. We formulate a simple but accurate semiclassical model for incorporating multidimensional tunneling in classical trajectory simulations. This model is based on the existence of locally conserved actions around the saddle point region on a multidimensional potential energy surface. Using classical perturbation theory and monitoring the imaginary action as a function of time along a classical trajectory we calculate state-specific unimolecular decay rates for a model two dimensional potential with coupling. Results are in good comparison with exact quantum results for the potential over a wide range of coupling constants. We propose a new semiclassical hybrid method to calculate state-to-state S-matrix elements for bimolecular reactive scattering. The accuracy of the Van Vleck-Gutzwiller propagator and the short time dynamics of the system make this method self-consistent and accurate. We also go beyond the stationary phase approximation by doing the resulting integrals exactly (numerically). As a result, classically forbidden probabilties are calculated with purely real time classical trajectories within this approach. Application to the one dimensional Eckart barrier demonstrates the accuracy of this approach. Successful application of the semiclassical hybrid approach to collinear reactive scattering is prevented by the phenomenon of chaotic scattering. The modified Filinov approach to evaluating the integrals is discussed, but application to collinear systems requires a more careful analysis. In three and higher dimensional scattering systems, chaotic scattering is suppressed and hence the accuracy and usefulness of the semiclassical method should be tested for such systems.

  6. Plasmon-assisted chemical reactions revealed by high-vacuum tip-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Lu, Shuaicheng; Sheng, Shaoxiang; Zhang, Zhenglong; Xu, Hongxing; Zheng, Hairong

    2014-08-01

    Tip-enhanced Raman spectroscopy (TERS) is the technique that combines the nanoscale spatial resolution of a scanning probe microscope and the highly sensitive Raman spectroscopy enhanced by the surface plasmons. It is suitable for chemical analysis at nanometer scale. Recently, TERS exhibited powerful potential in analyzing the chemical reactions at nanoscale. The high sensitivity and spatial resolution of TERS enable us to learn the reaction processes more clearly. More importantly, the chemical reaction in TERS is assisted by surface plasmons, which provides us an optical method to manipulate the chemical reactions at nanoscale. Here using our home-built high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup, we successfully observed the plasmon-assisted molecule dimerization and dissociation reactions. In HV-TERS system, under laser illumination, 4-nitrobenzenethiol (4NBT) molecules can be dimerized to p,p'-dimercaptoazobenzene (DMAB), and dissociation reaction occurs for malachite green (MG) molecules. Using our HV-TERS setup, the dynamic processes of the reactions are clearly revealed. The chemical reactions can be manipulated by controlling the plasmon intensity through changing the power of the incident laser, the tunneling current and the bias voltage. We also investigated the role of plasmonic thermal effect in the reactions by measuring both the Stokes and anti- Stokes Raman peaks. Our findings extend the applications of TERS, which can help to study the chemical reactions and understand the dynamic processes at single molecular level, and even design molecules by the plasmon-assisted chemical reactions.

  7. Chemical reactions between muonium and porphyrins

    NASA Astrophysics Data System (ADS)

    Jean, Y. C.; Ng, B. W.; Walker, D. C.

    1980-11-01

    The rate constants for reaction of muonium atoms with hemin and the protoporphyrin are found to be 2.7 10 9 and 6 10 8 M -1 s -1, respectively. The reaction mechanisms are mainly through the addition to the conjugated double bond for the protoporphyrin and by reductions or partial spin conversion processes for the hemin solutions. The point of reaction is suggested to be the peripheral site of the porphyrin molecules.

  8. On the rate of relativistic surface chemical reactions.

    PubMed

    Veitsman, E V

    2004-07-15

    On the basis of special relativity and the classical theory of chemical reaction rates it is shown how the surface chemical reaction rates vary as v --> c, where v is the velocity of the object under study and c is the velocity of light. PMID:15178286

  9. Chemical kinetics computer program for static and flow reactions

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

  10. Single-collision studies of energy transfer and chemical reaction

    SciTech Connect

    Valentini, J.J.

    1993-12-01

    The research focus in this group is state-to-state dynamics of reaction and energy transfer in collisions of free radicals such as H, OH, and CH{sub 3} with H{sub 2}, alkanes, alcohols and other hydrogen-containing molecules. The motivation for the work is the desire to provide a detailed understanding of the chemical dynamics of prototype reactions that are important in the production and utilization of energy sources, most importantly in combustion. The work is primarily experimental, but with an important and growing theoretical/computational component. The focus of this research program is now on reactions in which at least one of the reactants and one of the products is polyatomic. The objective is to determine how the high dimensionality of the reactants and products differentiates such reactions from atom + diatom reactions of the same kinematics and energetics. The experiments use highly time-resolved laser spectroscopic methods to prepare reactant states and analyze the states of the products on a single-collision time scale. The primary spectroscopic tool for product state analysis is coherent anti-Stokes Raman scattering (CARS) spectroscopy. CARS is used because of its generality and because the extraction of quantum state populations from CARS spectra is straightforward. The combination of the generality and easy analysis of CARS makes possible absolute cross section measurements (both state-to-state and total), a particularly valuable capability for characterizing reactive and inelastic collisions. Reactant free radicals are produced by laser photolysis of appropriate precursors. For reactant vibrational excitation stimulated Raman techniques are being developed and implemented.

  11. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Describes a dramatic chemical demonstration in which chemicals that are black and white combine to produce a colorless liquid. Reactants include tincture of iodine, bleach, white vinegar, Epsom salt, vitamin C tablets, and liquid laundry starch. (DDR)

  12. Mesoscale simulations of shockwave energy dissipation via chemical reactions.

    PubMed

    Antillon, Edwin; Strachan, Alejandro

    2015-02-28

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock. PMID:25725713

  13. Mesoscale simulations of shockwave energy dissipation via chemical reactions

    NASA Astrophysics Data System (ADS)

    Antillon, Edwin; Strachan, Alejandro

    2015-02-01

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock.

  14. Chemical Looping Combustion Reactions and Systems

    SciTech Connect

    Sarofim, Adel; Lighty, JoAnn; Smith, Philip; Whitty, Kevin; Eyring, Edward; Sahir, Asad; Alvarez, Milo; Hradisky, Michael; Clayton, Chris; Konya, Gabor; Baracki, Richard; Kelly, Kerry

    2011-07-01

    Chemical Looping Combustion (CLC) is one promising fuel-combustion technology, which can facilitate economic CO2 capture in coal-fired power plants. It employs the oxidation/reduction characteristics of a metal, or oxygen carrier, and its oxide, the oxidizing gas (typically air) and the fuel source may be kept separate. This work focused on two classes of oxygen carrier, one that merely undergoes a change in oxidation state, such as Fe3O4/Fe2O3 and one that is converted from its higher to its lower oxidation state by the release of oxygen on heating, i.e., CuO/Cu2O. This topical report discusses the results of four complementary efforts: (1) the development of process and economic models to optimize important design considerations, such as oxygen carrier circulation rate, temperature, residence time; (2) the development of high-performance simulation capabilities for fluidized beds and the collection, parameter identification, and preliminary verification/uncertainty quantification (3) the exploration of operating characteristics in the laboratory-scale bubbling bed reactor, with a focus on the oxygen carrier performance, including reactivity, oxygen carrying capacity, attrition resistance, resistance to deactivation, cost and availability (4) the identification of mechanisms and rates for the copper, cuprous oxide, and cupric oxide system using thermogravimetric analysis.

  15. Chemical redox reactions in ES-MS: Study of electrode reactions

    SciTech Connect

    Zhou, Feimeng; VAn Berkel, G.J.

    1995-12-31

    The authors previously demonstrated that chemical redox reactions can be used to ionize neutral commpounds for electrospray mass spectrometric (ES-MS) detection. Two different compounds, viz, C{sub 60}F{sub 48} and {beta}-carotene were used to demonstrate the utility of chemical redox reactions with on-line ES-MS for the elucidation of mechanisms of complicated electron transfer reactions and for the kinetic study of electrode reactions in which relatively short-lived intermediates are involved.

  16. An Analysis of the Algebraic Method for Balancing Chemical Reactions.

    ERIC Educational Resources Information Center

    Olson, John A.

    1997-01-01

    Analyzes the algebraic method for balancing chemical reactions. Introduces a third general condition that involves a balance between the total amount of oxidation and reduction. Requires the specification of oxidation states for all elements throughout the reaction. Describes the general conditions, the mathematical treatment, redox reactions, and

  17. An Analysis of the Algebraic Method for Balancing Chemical Reactions.

    ERIC Educational Resources Information Center

    Olson, John A.

    1997-01-01

    Analyzes the algebraic method for balancing chemical reactions. Introduces a third general condition that involves a balance between the total amount of oxidation and reduction. Requires the specification of oxidation states for all elements throughout the reaction. Describes the general conditions, the mathematical treatment, redox reactions, and…

  18. The How and Why of Chemical Reactions

    ERIC Educational Resources Information Center

    Schubert, Leo

    1970-01-01

    Presents a discussion of some of the fundamental concepts in thermodynamics and quantum mechanics including entropy, enthalpy, free energy, the partition function, chemical kinetics, transition state theory, the making and breaking of chemical bonds, electronegativity, ion sizes, intermolecular energies and of their role in explaining the nature…

  19. The How and Why of Chemical Reactions

    ERIC Educational Resources Information Center

    Schubert, Leo

    1970-01-01

    Presents a discussion of some of the fundamental concepts in thermodynamics and quantum mechanics including entropy, enthalpy, free energy, the partition function, chemical kinetics, transition state theory, the making and breaking of chemical bonds, electronegativity, ion sizes, intermolecular energies and of their role in explaining the nature

  20. FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

  1. Chemical Reaction Experiment for the Undergraduate Laboratory.

    ERIC Educational Resources Information Center

    Kwon, K. C.; And Others

    1987-01-01

    Provides an overview of an experiment on reaction kinetics of the anthracene-hydrogen system. Includes a description of the laboratory equipment, procedures, and data analysis requirements. Points out the advantages of the recommended technique. (ML)

  2. Systems of Chemical Equations as Reasonable Reaction Mechanisms

    NASA Astrophysics Data System (ADS)

    Dorozhkin, Sergey V.

    2001-07-01

    This paper demonstrates that chemical equations may be operated like a kind of LEGO game, with construction of the systems of chemical equations. In my teaching experience, these systems of chemical equations are able to help students to understand the reaction routes. Six general principles of creating the systems are formulated. Three examples from inorganic chemistry are considered and discussed in detail.

  3. Kinetics of Chemical Reactions in Flames

    NASA Technical Reports Server (NTRS)

    Zeldovich, Y.; Semenov, N.

    1946-01-01

    In part I of the paper the theory of flame propagation is developed along the lines followed by Frank-Kamenetsky and one of the writers. The development of chain processes in flames is considered. A basis is given for the application of the method of stationary concentrations to reactions in flames; reactions with branching chains are analyzed. The case of a diffusion coefficient different from the coefficient of temperature conductivity is considered.

  4. Nonequilibrium thermodynamics and a fluctuation theorem for individual reaction steps in a chemical reaction network

    NASA Astrophysics Data System (ADS)

    Pal, Krishnendu; Das, Biswajit; Banerjee, Kinshuk; Gangopadhyay, Gautam

    2015-09-01

    We have introduced an approach to nonequilibrium thermodynamics of an open chemical reaction network in terms of the propensities of the individual elementary reactions and the corresponding reverse reactions. The method is a microscopic formulation of the dissipation function in terms of the relative entropy or Kullback-Leibler distance which is based on the analogy of phase space trajectory with the path of elementary reactions in a network of chemical process. We have introduced here a fluctuation theorem valid for each opposite pair of elementary reactions which is useful in determining the contribution of each sub-reaction on the nonequilibrium thermodynamics of overall reaction. The methodology is applied to an oligomeric enzyme kinetics at a chemiostatic condition that leads the reaction to a nonequilibrium steady state for which we have estimated how each step of the reaction is energy driven or entropy driven to contribute to the overall reaction.

  5. A Case Study in Chemical Kinetics: The OH + CO Reaction.

    ERIC Educational Resources Information Center

    Weston, Ralph E., Jr.

    1988-01-01

    Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

  6. CW CO2 Laser Induced Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Pola, Joseph

    1989-05-01

    CW CO2 laser driven reactions between sulfur hexafluoride and carbon oxide, carbon suboxide, carbonyl sulfide and carbon disulfide proceed at subatmospheric pressures and yield fluorinated carbon compounds and sulfur tetrafluoride. CW CO2 laser driven reactions of organic compounds in the presence of energy-conveying sulfur hexafluoride show reaction course different from that normally observed due to elimination of reactor hot surface effects. The examples concern the decomposition of polychlorohydrocarbons, 2-nitropropane, tert.-butylamine, allyl chloride, spirohexane, isobornyl acetate and the oxidation of haloolefins. CW CO2 laser induced fragmentation of 1-methyl-l-silacyclobutanes and 4-silaspiro(3.4)octane in the presence of sulfur hexafluoride is an effective way for preparation and deposition of stable organosilicon polymers.

  7. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Walch, Stephen P.

    1992-01-01

    The work on the NH + NO system which was described in the last progress report was written up and a draft of the manuscript is included in the appendix. The appendix also contains a draft of a manuscript on an Ar + H + H surface. New work which was completed in the last six months includes the following: (1) calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction; (2) calculations for the NH2 + O reaction; (3) calculations for the CH3 + O2 reaction; and (4) calculations for CH3O and the two decomposition channels--CH2OH and H + H2CO. Detailed descriptions of this work will be given in manuscripts; however, brief descriptions of the CH3 + OH and CH3 + O2 projects are given.

  8. Non-equilibrium effects in high temperature chemical reactions

    NASA Technical Reports Server (NTRS)

    Johnson, Richard E.

    1987-01-01

    Reaction rate data were collected for chemical reactions occurring at high temperatures during reentry of space vehicles. The principle of detailed balancing is used in modeling kinetics of chemical reactions at high temperatures. Although this principle does not hold for certain transient or incubation times in the initial phase of the reaction, it does seem to be valid for the rates of internal energy transitions that occur within molecules and atoms. That is, for every rate of transition within the internal energy states of atoms or molecules, there is an inverse rate that is related through an equilibrium expression involving the energy difference of the transition.

  9. Developing Secondary Students' Conceptions of Chemical Reactions: The Introduction of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico; Dekkers, Hetty

    1998-01-01

    Describes an empirical study concerning the introduction of the concept of chemical equilibrium in chemistry classrooms in a way which challenges students' initial conceptions of chemical reactions. Contains 23 references. (DDR)

  10. 29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH FORMER GENERAL OFFICE BUILDING IN BACKGROUND. - U.S. Steel Duquesne Works, Fuel & Utilities Plant, Along Monongahela River, Duquesne, Allegheny County, PA

  11. CHEMICAL REACTIONS SIMULATED BY GROUND-WATER-QUALITY MODELS.

    USGS Publications Warehouse

    Grove, David B.; Stollenwerk, Kenneth G.

    1987-01-01

    Recent literature concerning the modeling of chemical reactions during transport in ground water is examined with emphasis on sorption reactions. The theory of transport and reactions in porous media has been well documented. Numerous equations have been developed from this theory, to provide both continuous and sequential or multistep models, with the water phase considered for both mobile and immobile phases. Chemical reactions can be either equilibrium or non-equilibrium, and can be quantified in linear or non-linear mathematical forms. Non-equilibrium reactions can be separated into kinetic and diffusional rate-limiting mechanisms. Solutions to the equations are available by either analytical expressions or numerical techniques. Saturated and unsaturated batch, column, and field studies are discussed with one-dimensional, laboratory-column experiments predominating. A summary table is presented that references the various kinds of models studied and their applications in predicting chemical concentrations in ground waters.

  12. Chemical pathways in ultracold reactions of SrF molecules

    NASA Astrophysics Data System (ADS)

    Meyer, Edmund R.; Bohn, John L.

    2011-03-01

    We present a theoretical investigation of the chemical reaction SrF + SrF → products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF → Sr2 + F2 is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF → SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule “handing off” a fluorine atom to the other molecule.

  13. Chemical pathways in ultracold reactions of SrF molecules

    NASA Astrophysics Data System (ADS)

    Meyer, Edmund; Bohn, John

    2011-05-01

    We present a theoretical investigation of the chemical reaction SrF + SrF --> products, focusing on reactions at ultralow temperatures. We find that bond swapping, SrF + SrF --> Sr2 + F2, is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF --> SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless, and proceeds by one SrF molecule ``handing off'' a fluorine atom to the other molecule. Supported by the NSF

  14. Analysis of weblike network structures of directed graphs for chemical reactions in methane plasmas

    NASA Astrophysics Data System (ADS)

    Sakai, Osamu; Nobuto, Kyosuke; Miyagi, Shigeyuki; Tachibana, Kunihide

    2015-10-01

    Chemical reactions of molecular gases like methane are so complicated that a chart of decomposed and/or synthesized species originating from molecules in plasma resembles a weblike network in which we write down species and reactions among them. Here we consider properties of the network structures of chemical reactions in methane plasmas. In the network, atoms/molecules/radical species are assumed to form nodes and chemical reactions correspond to directed edges in the terminology of graph theory. Investigation of the centrality index reveals importance of CH3 in the global chemical reaction, and difference of an index for each radical species between cases with and without electrons clarifies that the electrons are at an influential position to tighten the network structure.

  15. Molecular dynamics study of phase separation in fluids with chemical reactions

    NASA Astrophysics Data System (ADS)

    Krishnan, Raishma; Puri, Sanjay

    2015-11-01

    We present results from the first d =3 molecular dynamics (MD) study of phase-separating fluid mixtures (AB) with simple chemical reactions (A ?B ). We focus on the case where the rates of forward and backward reactions are equal. The chemical reactions compete with segregation, and the coarsening system settles into a steady-state mesoscale morphology. However, hydrodynamic effects destroy the lamellar morphology which characterizes the diffusive case. This has important consequences for the phase-separating structure, which we study in detail. In particular, the equilibrium length scale (?eq) in the steady state suggests a power-law dependence on the reaction rate ? :?eq?-? with ? ?1.0 .

  16. Parameter estimation in complex flows with chemical reactions

    NASA Astrophysics Data System (ADS)

    Robinson, Daniel J.

    The estimation of unknown parameters in engineering and scientific models continues to be of great importance in order to validate them to available experimental data. These parameters of concern cannot be known beforehand, but must be measured experimentally, variables such as chemical species concentrations, pressures, or temperatures as examples. Particularly, in chemically reacting flows, the estimation of kinetic rate parameters from experimentally determined values is in great demand and not well understood. New parameter optimization algorithms have been developed from a Gauss-Newton formulation for the estimation of reaction rate parameters in several different complex flow applications. A zero-dimensional parameter estimation methodology was used in conjunction with a parameter sensitivity study and then applied to three-dimensional flow models. This new parameter estimation technique was applied to three-dimensional models for chemical vapor deposition of silicon carbide and gallium arsenide semiconductor materials. The parameter estimation for silicon carbide for several different operating points was in close agreement to experiment. The parameter estimation for gallium arsenide proved to be very accurate, being within four percent of the experimental data. New parameter estimation algorithms were likewise created for a three-dimensional multiphase model for methanol spray combustion. The kinetic rate parameters delivered results in close agreement to experiment for profiles of combustion species products. In addition, a new parameter estimation method for the determination of spray droplet sizes and velocities is presented. The results for methanol combustion chemical species profiles are in good agreement to experiment for several different droplet sizes. Lastly, the parameter estimation method was extended to a bio-kinetic application, namely mitochondrial cells, that are cardiac or respiratory cells found in animals and humans. The results for the electrochemical parameters examined again show very close agreement to the experimental values. The usual method of determining chemical reaction rates by measurement is lengthy and time consuming, especially where the chemistry and chemical processes are of a more complex nature. This computational method and associated algorithms has shown to deliver accurate correlations to the experimental data for three-dimensional models, demonstrated in these new unique applications of the technique.

  17. Quantifying chemical reactions by using mixing analysis.

    PubMed

    Jurado, Anna; Vzquez-Su, Enric; Carrera, Jess; Tubau, Isabel; Pujades, Estanislao

    2015-01-01

    This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. We propose an approach to quantify such processes using mixing calculations. The methodology consists of the following steps: (1) identification of the recharge sources (end-members) and selection of the species (conservative and non-conservative) to be used, (2) identification of the chemical processes and (3) evaluation of mixing ratios including the chemical processes. This methodology has been applied in the Bess River Delta (NE Barcelona, Spain), where the River Bess is the main aquifer recharge source. A total number of 51 groundwater samples were collected from July 2007 to May 2010 during four field campaigns. Three river end-members were necessary to explain the temporal variability of the River Bess: one river end-member is from the wet periods (W1) and two are from dry periods (D1 and D2). This methodology has proved to be useful not only to compute the mixing ratios but also to quantify processes such as calcite and magnesite dissolution, aerobic respiration and denitrification undergone at each observation point. PMID:25280248

  18. Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks

    ERIC Educational Resources Information Center

    Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

    2011-01-01

    Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to

  19. Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks

    ERIC Educational Resources Information Center

    Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

    2011-01-01

    Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to…

  20. Laser cutting with chemical reaction assist

    DOEpatents

    Gettemy, D.J.

    1992-11-17

    A method is described for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation. 1 figure.

  1. METHODOLOGICAL NOTES: Brusselator an abstract chemical reaction?

    NASA Astrophysics Data System (ADS)

    Lavrova, Anastasiya I.; Postnikov, E. B.; Romanovsky, Yurii M.

    2009-12-01

    In this paper we consider the Brusselator and the Sel'kov model, which describes the irreversible reaction of glycolysis in the regime of self-sustained oscillations. We show that these two differently constructed models can be reduced to a single equation a generalized Rayleigh equation. The physical basis for this generality is investigated. The advantages of this equation as a tool for qualitative and quantitative analyses, as well as the similarities and differences of the solutions realized for each of the two concrete models in the cases of almost harmonic and relaxation self-sustained oscillations, are discussed.

  2. Laser cutting with chemical reaction assist

    DOEpatents

    Gettemy, Donald J. (Los Alamos, NM)

    1992-01-01

    A method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation.

  3. Ozone - plant surface reactions an important ozone loss term?

    NASA Astrophysics Data System (ADS)

    Hansel, Armin; Jud, Werner; Fischer, Lukas; Canaval, Eva; Wohlfahrt, Georg; Tissier, Alain

    2015-04-01

    Elevated tropospheric ozone concentrations are considered a toxic threat to plants responsible for global crop losses with associated economic costs of several billions dollar per year. Plant injuries have been related to the uptake of ozone through stomatal pores and oxidative effects damaging the internal leaf tissue. But a striking question remains: How much ozone enters the plant through open stomata and how much ozone is lost by chemical reactions at the plant surface? Until now surface losses are estimated from measured total ozone deposition fluxes and calculated stomatal conductance values. While stomatal conductance of CO2 and H2O is well understood and extensively used in describing plant atmosphere gas exchange, stomatal conductance of ozone is not well known. Here we use different Nicotiana tabacum varieties and find that surface reactions of ozone with diterpenoids synthesized by glandular trichomes reduce ozone flux through open stomata. Our measurements reveal that fast ozone loss at the plant surface is accompanied with prompt release of oxygenated volatile compounds. In the ozone fumigation experiments of different Nicotiana tabacum varieties the release of specific volatile oxy-VOCs allowed to identify the semi volatile precursor compounds at the plant surface. Ozone fumigation experiments with Norway spruce (Picea abies) and Scots Pine (Pinus sylvestris), two common species in the Northern Hemisphere, show also a significant ozone loss at the plant surface for Picea abies. Fluid dynamic calculations of ozone transport in the diffusive leaf boundary layer reveal a vertical but no horizontal ozone gradient thus reducing ozone fluxes through the pores in case of efficient ozone scavenging plant surfaces. We explain this efficient ozone protection mechanism by the porous surface architecture of plants in combination with unsaturated semi-volatile compounds deposited at the plant surface. These results show that unsaturated semi-volatile compounds at the plant surface should be considered as oxygenated VOC source, impacting gas phase chemistry, as well as efficient ozone sink improving the plant's ozone tolerance

  4. Elementary reaction modeling of solid oxide electrolysis cells: Main zones for heterogeneous chemical/electrochemical reactions

    NASA Astrophysics Data System (ADS)

    Li, Wenying; Shi, Yixiang; Luo, Yu; Cai, Ningsheng

    2015-01-01

    A theoretical model of solid oxide electrolysis cells considering the heterogeneous elementary reactions, electrochemical reactions and the transport process of mass and charge is applied to study the relative performance of H2O electrolysis, CO2 electrolysis and CO2/H2O co-electrolysis and the competitive behavior of heterogeneous chemical and electrochemical reactions. In cathode, heterogeneous chemical reactions exist near the outside surface and the electrochemical reactions occur near the electrolyte. According to the mathematical analysis, the mass transfer flux D ?c determines the main zone size of heterogeneous chemical reactions, while the charge transfer flux ? ?V determines the other one. When the zone size of heterogeneous chemistry is enlarged, more CO2 could react through heterogeneous chemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to H2O electrolysis. Meanwhile, when the zone size of electrochemistry is enlarged, more CO2 could react through electrochemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to CO2 electrolysis. The relative polarization curves, the ratio of CO2 participating in electrolysis and heterogeneous chemical reactions, the mass and charge transfer flux and heterogeneous chemical/electrochemical reaction main zones are simulated to study the effects of cathode material characteristics (porosity, particle diameter and ionic conductivity) and operating conditions (gas composition and temperature).

  5. Results of the 2010 Survey on Teaching Chemical Reaction Engineering

    ERIC Educational Resources Information Center

    Silverstein, David L.; Vigeant, Margot A. S.

    2012-01-01

    A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the

  6. Results of the 2010 Survey on Teaching Chemical Reaction Engineering

    ERIC Educational Resources Information Center

    Silverstein, David L.; Vigeant, Margot A. S.

    2012-01-01

    A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the…

  7. Flow Tube Studies of Gas Phase Chemical Processes of Atmospheric Importance

    NASA Technical Reports Server (NTRS)

    Molina, Mario J.

    1997-01-01

    The objective of this project is to conduct measurements of elementary reaction rate constants and photochemistry parameters for processes of importance in the atmosphere. These measurements are being carried out under temperature and pressure conditions covering those applicable to the stratosphere and upper troposphere, using the chemical ionization mass spectrometry turbulent flow technique developed in our laboratory.

  8. Inorganic chemicals in an effluent-dominated stream as indicators for chemical reactions and streamflows

    NASA Astrophysics Data System (ADS)

    Kim, Kangjoo; Lee, Ji Sun; Oh, Chang-Whan; Hwang, Gab-Soo; Kim, Jinsam; Yeo, Sungku; Kim, Yeongkyoo; Park, Seongmin

    2002-07-01

    The chemical behavior of major inorganic ions in the streams of the Mankyung River area (South Korea) was investigated. Mixing with effluent from the Jeonju STP (a municipal sewage treatment plant in Jeonju City) was the most important process in regulating the water chemistry of the streams. The effluent was chemically distinct relative to the stream waters in inorganic composition. Behavior of various ions was evaluated by comparing their concentrations with the concentration of chloride, a conservative chemical species. It was revealed that concentrations of chloride and sulfate, the total concentration of major cations, and electrical conductivity in the stream were controlled only by mixing, indicating their conservative behavior similar to chloride. Alkalinity and concentration of nitrate, however, were regulated by various reactions such as mixing, photosynthesis, respiration, and decomposition of organic matter. Streamflows were estimated by observing chemical composition of the effluent and those of up/downstream waters. Estimated flows based on the conservative chemical parameters were nearly the same as those directly measured using an area-velocity method, indicating the validity of the chemistry-based method.

  9. Laboratory Studies of Homogeneous and Heterogeneous Chemical Processes of Importance in the Upper Atmosphere

    NASA Technical Reports Server (NTRS)

    Molina, Mario J.

    2003-01-01

    The objective of this study was to conduct measurements of chemical kinetics parameters for reactions of importance in the stratosphere and upper troposphere, and to study the interaction of trace gases with ice surfaces in order to elucidate the mechanism of heterogeneous chlorine activation processes, using both a theoretical and an experimental approach. The measurements were carried out under temperature and pressure conditions covering those applicable to the stratosphere and upper troposphere. The main experimental technique employed was turbulent flow-chemical ionization mass spectrometry, which is particularly well suited for investigations of radical-radical reactions.

  10. Molecular switch based on a biologically important redox reaction.

    PubMed

    Yan, Ping; Holman, Michael W; Robustelli, Paul; Chowdhury, Arindam; Ishak, Fady I; Adams, David M

    2005-01-13

    Building on our earlier report of a single-molecule probe, we show how biologically important redox centers, nicotinamide and quinone, incorporated into a fluorophore-spacer-receptor molecular structure, form redox active molecular switches, with the photoinduced electron-transfer behavior of each depending on the oxidation state of the receptor subunit. The switch based on nicotinamide (3/6) is strongly fluorescent in its oxidized state (Phi(F) approximately 1.0) but nonfluorescent in the reduced state (Phi(F) < 0.001) due to electron transfer from the reduced nicotinamide to the photoexcited fluorophore. The fluorescence can be reversibly switched off and on chemically by successive reduction with NaBH(3)CN and oxidation with tetrachlorobenzoquinone and switched electrochemically over 10 cycles without significant degradation. A similar switch based on quinonimine turned out to be nonfluorescent in both reduced and oxidized states: in addition to a similar quenching mechanism in the reduced state, quenching also occurs in the oxidized state, due to electron transfer from the fluorophore to the receptor. Ab initio quantum chemical calculations of orbital energy levels were used to corroborate these quenching mechanisms. Calculations predicted photoinduced electron transfer to be energetically favorable in all cases where quenching was observed and unfavorable in all cases where it was not. Application of the perylene analogue as a biosensor has also been demonstrated by coupling the switch to the catalytic pathway of yeast alcohol dehydrogenase, a common NADH/NAD(+)-utilizing enzyme. PMID:16850995

  11. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1988-01-01

    The minimum energy path for the addition of a hydrogen atom to N2 is characterized in CASSCF/CCI calculations using the (4s3p2d1f/3s2p1d) basis set, with additional single point calculations at the stationary points of the potential energy surface using the (5s4p3d2f/4s3p2d) basis set. These calculations represent the most extensive set of ab initio calculations completed to date, yielding a zero point corrected barrier for HN2 dissociation of approx. 8.5 kcal mol/1. The lifetime of the HN2 species is estimated from the calculated geometries and energetics using both conventional Transition State Theory and a method which utilizes an Eckart barrier to compute one dimensional quantum mechanical tunneling effects. It is concluded that the lifetime of the HN2 species is very short, greatly limiting its role in both termolecular recombination reactions and combustion processes.

  12. Matrix isolation as a tool for studying interstellar chemical reactions

    NASA Technical Reports Server (NTRS)

    Ball, David W.; Ortman, Bryan J.; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques.

  13. Asymmetric chemical reactions by polarized quantum beams

    NASA Astrophysics Data System (ADS)

    Takahashi, Jun-Ichi; Kobayashi, Kensei

    One of the most attractive hypothesis for the origin of homochirality in terrestrial bio-organic compounds (L-amino acid and D-sugar dominant) is nominated as "Cosmic Scenario"; a chiral impulse from asymmetric excitation sources in space triggered asymmetric reactions on the surfaces of such space materials as meteorites or interstellar dusts prior to the existence of terrestrial life. 1) Effective asymmetric excitation sources in space are proposed as polarized quantum beams, such as circularly polarized light and spin polarized electrons. Circularly polarized light is emitted as synchrotron radiation from tightly captured electrons by intense magnetic field around neutron stars. In this case, either left-or right-handed polarized light can be observed depending on the direction of observation. On the other hand, spin polarized electrons is emitted as beta-ray in beta decay from radioactive nuclei or neutron fireballs in supernova explosion. 2) The spin of beta-ray electrons is longitudinally polarized due to parity non-conservation in the weak interaction. The helicity (the the projection of the spin onto the direction of kinetic momentum) of beta-ray electrons is universally negative (left-handed). For the purpose of verifying the asymmetric structure emergence in bio-organic compounds by polarized quantum beams, we are now carrying out laboratory simulations using circularly polarized light from synchrotron radiation facility or spin polarized electron beam from beta-ray radiation source. 3,4) The target samples are solid film or aqueous solution of racemic amino acids. 1) K.Kobayashi, K.Kaneko, J.Takahashi, Y.Takano, in Astrobiology: from simple molecules to primitive life; Ed. V.Basiuk; American Scientific Publisher: Valencia, 2008. 2) G.A.Gusev, T.Saito, V.A.Tsarev, A.V.Uryson, Origins Life Evol. Biosphere. 37, 259 (2007). 3) J.Takahashi, H.Shinojima, M.Seyama, Y.Ueno, T.Kaneko, K.Kobayashi, H.Mita, M.Adachi, M.Hosaka, M.Katoh, Int. J. Mol. Sci. 10, 3044 (2009). 4) V.I.Burkov, L.A.Goncharova, G.A.Gusev, H.Hashimoto, F.Kaneko, T.Kaneko, K. Kobayashi, H.Mita, E.V.Moiseenko, T.Ogawa, N.G.Poluhina, T.Saito, S.Shima, J.Takahashi, M.Tanaka, Y.Tao, V.A.Tsarev, J.Xu, H.Yabuta, K.Yagi-Watanabe, H.Yan, G.Zhang, Origins Life Evol. Biosphere, 39 295 (2009).

  14. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    PubMed Central

    2015-01-01

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys.2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum under DFT by several fold. The approach also shows promise for free energy calculations when thermal noise can be controlled. PMID:25516726

  15. International chemical identifier for reactions (RInChI).

    PubMed

    Grethe, Guenter; Goodman, Jonathan M; Allen, Chad Hg

    2013-01-01

    The IUPAC International Chemical Identifier (InChI) provides a method to generate a unique text descriptor of molecular structures. Building on this work, we report a process to generate a unique text descriptor for reactions, RInChI. By carefully selecting the information that is included and by ordering the data carefully, different scientists studying the same reaction should produce the same RInChI. If differences arise, these are most likely the minor layers of the InChI, and so may be readily handled. RInChI provides a concise description of the key data in a chemical reaction, and will help enable the rapid searching and analysis of reaction databases. PMID:24152584

  16. Method and apparatus for controlling gas evolution from chemical reactions

    DOEpatents

    Skorpik, J.R.; Dodson, M.G.

    1999-05-25

    The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846. 8 figs.

  17. Method and apparatus for controlling gas evolution from chemical reactions

    DOEpatents

    Skorpik, James R.; Dodson, Michael G.

    1999-01-01

    The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846.

  18. Chemical reactions in viscous liquids under space conditions

    NASA Astrophysics Data System (ADS)

    Kondyurin, A.; Lauke, B.; Richter, E.

    A long-term human flight needs a large-size space ships with artificial self-regulating ecological life-support system. The best way for creation of large-size space ship is a synthesis of light construction on Earth orbit, that does not need a high energy transportation carriers from Earth surface. The construction can be created by the way of chemical polymerisation reaction under space environment. But the space conditions are very specific for chemical reactions. A high vacuum, high energy particles, X-rays, UV- and VUV-irradiations, atomic oxygen, microgravity have a significant influence on chemical reactions. Polymerisation reactions in liquid active mixture were studied in simulated space environment. The epoxy resins based on Bisphenol A and amine curing agents were investigated under vacuum, microwave plasma discharge and ion beam. An acceleration of polymerisation reaction with free radicals formation was observed. The polymerisation reaction can be carried out under space environment. The study was supported by Alexander von Humboldt Foundation (A. Kondyurin) and European Space Agency, ESTEC (contract 17083/03/NL/Sfe "Space Environmental Effects on the Polymerisation of Composite Structures").

  19. Imaging of product molecule trajectories in chemical reactions

    NASA Astrophysics Data System (ADS)

    Cline, Joseph

    2000-06-01

    The combination of velocity-mapped ion imaging and polarized ionization spectroscopy makes possible detailed measurements of angular correlations arising in the molecular trajectories that characterize a chemical reaction mechanism. Of particular interest in reaction dynamics is the angular correlation between rotational angular momentum and velocity. This correlation contains the signature of "frisbee" and "propeller" molecular trajectories and, in special cases, preferred senses of product rotation arising from asymmetry in the reaction mechanism. We show techniques for extracting the recoil angle-dependent angular momentum polarization from ion images of a molecule recoiling from a chemical reaction. The angular momentum polarization of the nitric oxide (NO) molecule produced in chemical reactions is easily detected by polarized 1+1' resonance-enhanced multiphoton ionization: (1) Molecular photodissocation. Rotational alignment and orientation of NO is measured in correlation with recoil velocity in the photodissociation of NO2 and large nitrosoalkanes. The imaging data provides a beautifully clear picture of nuclear trajectories during the photodissociation. In the case of NO2 it is shown how preferred senses of rotation can be created in the photodissociation of an achiral molecule by linearly polarized light. (2) Bimolecular scattering. Angular correlations of velocity and rotational angular momentum are measured in rotationally inelastic collisions of NO with Ar. The imaging results show the resulting angular momentum polarization directly imposed on top of the Newton recoil sphere of the NO molecule. These results are interpreted in terms of simple models for the reaction mechanisms.

  20. Photon Antibunching in a Cyclic Chemical Reaction Scheme.

    PubMed

    Vester, Michael; Staut, Tobias; Enderlein, Jrg; Jung, Gregor

    2015-04-01

    The direct observation of chemical reactions on the single-molecule level is an ultimate goal in single-molecule chemistry, which also includes kinetic analyses. To analyze the lifetime of reaction intermediates, very sophisticated excitation schemes are often required. Here we focus on the kinetic analysis of the ground-state proton transfer within the photocycle of a photoacid. In detail, we demonstrate the determination of the bimolecular rate constant of this process with nanosecond resolution. The procedure relies on the exploration of a purely quantum-optical effect, namely, photon antibunching, and thus on evaluating interphoton arrival times to extract the reaction rate constant. PMID:26262964

  1. Chemical pathways in ultracold reactions of SrF molecules

    SciTech Connect

    Meyer, Edmund R.; Bohn, John L.

    2011-03-15

    We present a theoretical investigation of the chemical reaction SrF + SrF {yields} products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF {yields} Sr{sub 2} + F{sub 2} is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF {yields} SrF{sub 2} + Sr, and even then only singlet states of the SrF{sub 2} trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule ''handing off'' a fluorine atom to the other molecule.

  2. CHARACTERIZATION OF CHEMICALLY MODIFIED HYPERTHERMOPHILIC ENZYMES FOR CHEMICAL SYNTHESES AND BIOREMEDIATION REACTIONS

    EPA Science Inventory

    Research developments in the area of biocatalysis in organic solvents are expected to greatly expand the role of bioprocessing in chemical synthesis, fuel processing, and bioremediation technologies. Many biological transformation reactions of interest to DOE site remediation inv...

  3. Program Helps To Determine Chemical-Reaction Mechanisms

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Radhakrishnan, K.

    1995-01-01

    General Chemical Kinetics and Sensitivity Analysis (LSENS) computer code developed for use in solving complex, homogeneous, gas-phase, chemical-kinetics problems. Provides for efficient and accurate chemical-kinetics computations and provides for sensitivity analysis for variety of problems, including problems involving honisothermal conditions. Incorporates mathematical models for static system, steady one-dimensional inviscid flow, reaction behind incident shock wave (with boundary-layer correction), and perfectly stirred reactor. Computations of equilibrium properties performed for following assigned states: enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. Written in FORTRAN 77 with exception of NAMELIST extensions used for input.

  4. Dynamic control and information processing in chemical reaction systems by tuning self-organization behavior

    NASA Astrophysics Data System (ADS)

    Lebiedz, Dirk; Brandt-Pollmann, Ulrich

    2004-09-01

    Specific external control of chemical reaction systems and both dynamic control and signal processing as central functions in biochemical reaction systems are important issues of modern nonlinear science. For example nonlinear input-output behavior and its regulation are crucial for the maintainance of the life process that requires extensive communication between cells and their environment. An important question is how the dynamical behavior of biochemical systems is controlled and how they process information transmitted by incoming signals. But also from a general point of view external forcing of complex chemical reaction processes is important in many application areas ranging from chemical engineering to biomedicine. In order to study such control issues numerically, here, we choose a well characterized chemical system, the CO oxidation on Pt(110), which is interesting per se as an externally forced chemical oscillator model. We show numerically that tuning of temporal self-organization by input signals in this simple nonlinear chemical reaction exhibiting oscillatory behavior can in principle be exploited for both specific external control of dynamical system behavior and processing of complex information.

  5. On some dynamical diagrams of chemical reaction engineering.

    PubMed

    Aris, Rutherford

    1999-03-01

    A brief historical survey of some of the influential types of diagrams that have been used in chemical reaction engineering is given. These include the phase plane, the simple autocatalytic diagram, and the stroboscopic phase plane. (c) 1999 American Institute of Physics. PMID:12779797

  6. 2011 Chemical Reactions at Surfaces Gordon Research Conference

    SciTech Connect

    Peter Stair

    2011-02-11

    The Gordon Research Conference on Chemical Reactions at Surfaces is dedicated to promoting and advancing the fundamental science of interfacial chemistry and physics by providing surface scientists with the foremost venue for presentation and discussion of research occurring at the frontiers of their fields.

  7. Chemical Reaction Engineering: Current Status and Future Directions.

    ERIC Educational Resources Information Center

    Dudukovic, M. P.

    1987-01-01

    Describes Chemical Reaction Engineering (CRE) as the discipline that quantifies the interplay of transport phenomena and kinetics in relating reactor performance to operating conditions and input variables. Addresses the current status of CRE in both academic and industrial settings and outlines future trends. (TW)

  8. WATER AS A REACTION MEDIUM FOR CLEAN CHEMICAL PROCESSES.

    EPA Science Inventory

    Green chemistry is a rapid developing new field that provides us a pro-active avenue for the sustainable development of future science and technologies. When designed properly, clean chemical technology can be developed in water as a reaction media. The technologies generated f...

  9. Gas-phase reactions of halogen species of atmospheric importance

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm/molecule/s. The reaction between I and NO3 was found to occur at a rate of about 60 percent of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO3 was found to be (4.5 +/- 1.9) x 10(exp -10)/cu cm/molecule/s. An upper limit for the heat of formation of IONO2 of (21 +/- 3) kJmol(exp -1) was also derived.

  10. Emergence of heterogeneous structures in chemical reaction-diffusion networks.

    PubMed

    Xuan, Qi; Du, Fang; Wu, Tie-Jun; Chen, Guanrong

    2010-10-01

    This paper suggests that reaction-diffusion processes, rather than pure topological rules, are responsible for the emergence of heterogeneous structures of complex chemical reaction networks. In such a network, chemical substances react in each node and diffuse between connected nodes. At the same time, each node is able to sense the difference between its own state and the environmental conditions and can rearrange its neighbors via a local rewiring process so as to eliminate the sensed difference. Then, the network, even originally homogeneous, will develop a heterogeneous structure under certain environmental conditions. Such a resultant heterogeneous network may be disassortative, highly clustering, and small world as well. This implies that the reaction-diffusion equilibrium can be statistically controlled by slightly changing the structure of the underlying network. This structure-control mechanism may be especially useful in the situations where some other macroscopic measurements, such as temperature and pressure, are not allowed to be changed through the process. PMID:21230354

  11. Emergence of heterogeneous structures in chemical reaction-diffusion networks

    NASA Astrophysics Data System (ADS)

    Xuan, Qi; Du, Fang; Wu, Tie-Jun; Chen, Guanrong

    2010-10-01

    This paper suggests that reaction-diffusion processes, rather than pure topological rules, are responsible for the emergence of heterogeneous structures of complex chemical reaction networks. In such a network, chemical substances react in each node and diffuse between connected nodes. At the same time, each node is able to sense the difference between its own state and the environmental conditions and can rearrange its neighbors via a local rewiring process so as to eliminate the sensed difference. Then, the network, even originally homogeneous, will develop a heterogeneous structure under certain environmental conditions. Such a resultant heterogeneous network may be disassortative, highly clustering, and small world as well. This implies that the reaction-diffusion equilibrium can be statistically controlled by slightly changing the structure of the underlying network. This structure-control mechanism may be especially useful in the situations where some other macroscopic measurements, such as temperature and pressure, are not allowed to be changed through the process.

  12. Theoretical Chemical Dynamics Studies of Elementary Combustion Reactions

    SciTech Connect

    Donald L. Thompson

    2006-04-27

    The purpose of this research was the development and application of theoretical/computational methods for accurate predictions of the rates of reactions in many-atom systems. The specific aim was to improve computational methods for studying the chemical dynamics of large, complex systems and to obtain a better understanding of the chemical reactions involving large polyatomic molecules and radicals. The focus was on the development an automatic potential energy surface generation algorithm that takes advantage of high-performance computing environments; e.g., software for rate calculations that direct quantum chemistry codes to produce ab initio predictions of reaction rates and related dynamics quantities. Specifically, we developed interpolative moving least-squares (IMLS) methods for accurately fitting ab initio energies to provide global PESs and for use in direct dynamics simulations.

  13. Radical-neutral chemical reactions studied at low temperature with VUV synchrotron photoionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Soorkia, Satchin; Leone, Stephen R.; Wilson, Kevin R.

    2012-11-01

    A pulsed Laval nozzle apparatus employing tunable VUV synchrotron photoionization and quadrupole mass spectrometry for the study of radical-neutral chemical reactions of importance for modeling the atmosphere of Titan and the outer planets is described. The apparatus enables the study of low-temperature kinetics and isomer-resolved product branching of highly reactive radicals with unsaturated hydrocarbons reactions. The low-temperature branching ratio for the reaction of the ethynyl radical (C2H) with allene (C3H4) has been measured for the first time at 79 K. This reaction is found to yield 1,4-pentadiyne as the major reaction product (50+10%), followed by ethynylallene (28+10%) and methyldiacetylene (22+10%) via H-atom elimination from the initially formed C5H5 adduct. The derived branching ratios can be directly used to predict the chemical evolution of Titan's atmosphere.

  14. Students' Understandings of Chemical Bonds and the Energetics of Chemical Reactions.

    ERIC Educational Resources Information Center

    Boo, Hong Kwen

    1998-01-01

    Investigates Grade 12 students' understandings of the nature of chemical bonds and the energetics elicited across five familiar chemical reactions following a course of instruction. Discusses the many ways in which students can misconstruct concepts and principles. Contains 63 references. (DDR)

  15. Teaching Rates of Chemical Reactions and Chemical Equilibrium by Simulation Methods

    ERIC Educational Resources Information Center

    Fogliani, C. L.; Townsend, I. T.

    1977-01-01

    The authors give directions for comparing the rates of zero and first order chemical reactions to the rate of flowing water in simple physical systems. They also show how to compare chemical equilibrium to the level of water in a u-shaped tube. (AJ)

  16. Development of a chemical oxygen - iodine laser with production of atomic iodine in a chemical reaction

    SciTech Connect

    Censky, M; Spalek, O; Jirasek, V; Kodymova, J; Jakubec, I

    2009-11-30

    The alternative method of atomic iodine generation for a chemical oxygen - iodine laser (COIL) in chemical reactions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied. (lasers)

  17. PDF calculation of scalar mixing layer with simple chemical reactions

    NASA Astrophysics Data System (ADS)

    Kanzaki, Takao; Pope, Stephen B.

    1999-11-01

    A joint velocity-composition-turbulent frequency PDF(JPDF) model is used to simulate reactive mixing layer in a grid-generated turbulence with the influence of second-order irreversible chemical reactions. To investigate the effects of molecular mixing, a gas flow and a liquid flow are simulated. For a gas flow, the oxidation reaction (NO+ O3 arrow NO2 +O2 ) between nitricoxide (NO) and ozone (O3 ) is used. For a liquid flow, the saponification reaction(NaOH+HCOOCH3 arrow HCOONa+CH_3OH) between sodiumhydroxide(NaOH) and methylformate(HCOOCH_3) is used. The both cases are moderately fast reactions. Therefore, reactive scalar statistics are affected by turbulent mixing. The results of caliculation are compared with experimental data of Komori et al.(1994) and Bilger et al.(1991)

  18. Chemical research on red pigments after adverse reactions to tattoo.

    PubMed

    Tammaro, A; Toniolo, C; Giulianelli, V; Serafini, M; Persechino, S

    2016-03-01

    Currently, the incidence of tattooing is on the rise compared to the past, especially among adolescents, and it leads to the urgency of monitoring the security status of tattooing centers, as well as to inform people about the risks of tattoo practice. In our clinical experience, 20% of tattooed patients presented adverse reactions, like allergic contact dermatitis, psoriasis with Koebner's phenomena and granulomatous reactions, with the latter most prevalent and most often related to red pigment. Adverse reactions to tattoo pigments, especially the red one, are well known and described in literature. Great attention has to be focused on the pigments used, especially for the presence of new substances, often not well known. For this reason, we decided to perform a study on 12 samples of red tattoo ink, obtained by patients affected by different cutaneous reactions in the site of tattoo, to analyze their chemical composition. PMID:26934738

  19. The Electrochemical Thermodynamics for Chemical Reactions in Dispersed Cells.

    PubMed

    Yong-Qiang; Chun-Hui; Jin-Chuan

    1999-09-01

    There is a large specific surface area in a dispersed cell, so much so that there are some notable differences in thermodynamic quantities for a chemical reaction in the cell because of the strong surface effect. The thermodynamic relations between the electromotive force (emf) and the dispersity of a cell and between each of thermodynamic properties and the dispersivity of the cell are derived, and the effects of degree of dispersion of substances in the cell on the emf and the thermodynamic properties are discussed. The results show that the emf, the equilibrium constant, the entropy for reaction, the heat of reaction, and the enthalpy of reaction vary with the dispersivities of the reactants or/and the products in the cell. And two new concepts, surface emf and dispersion cell, are put forward in this paper. Copyright 1999 Academic Press. PMID:10441416

  20. Measurements of the Astrophysically Important 40Ca(?,?)44Ti Reaction

    NASA Astrophysics Data System (ADS)

    Robertson, Daniel; Gorres, J.; Collon, P.; Becker, H.; Wiescher, M.

    2012-05-01

    Observational studies of galactic ?-emitters such as 44Ti (t1/2 = 58.9 0.3 yrs) have highlighted their use in nucleosynthesis studies of massive stars both in their late stage stellar evolution and final explosive demise in core collapse supernova events. Models used in the simulation of such ? emitters rely heavily upon reliable reaction rates for both the creation and annihilation of these isotopes over large temperature ranges. The production of 44Ti mainly through the 40Ca(?,?)44Ti reaction is thought to take place mostly in the ?-rich freeze out phase of a core collapse supernova. However, current supernova model simulations predict lower 44Ti to 56Ni ratios than observed, creating a need for more information about its production mechanism. A number of previous experimental studies include prompt ?-ray measurements, recoil mass separator experiments and the use of accelerator mass spectrometry, all giving greatly different reaction rates. The results of experiments at the RUBION laboratory, Bochum and NSL, Notre Dame have allowed for greater constraints to be placed on reaction rates when compared to previous measurements. Acknowledgment and thanks to the support of the National Science Foundation (grant number PHYS-58100) and the Joint Institute for Nuclear Astrophysics (grant number PHY08-22648).

  1. INVESTIGATION OF IMPORTANT HYDROXYL RADICAL REACTIONS IN THE PERTURBED TROPOSPHERE

    EPA Science Inventory

    The flash-photolysis resonance fluorescence technique was used to study the reaction kinetics of hydroxyl radicals with ten aromatic and six olefinic hydrocarbons at 298 K and several diluent gas pressures. The aromatic compounds that were studied include benzene, toluene, ethylb...

  2. Gas-Phase Reactions of Halogen Species of Atmospheric Importance.

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) times 10 ^{-12}cm^{ -3}molecule^{-1}s ^{-1}. The reaction between I and NO_3 was found to occur at a rate of about 60% of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO_3 was found to be (4.5 +/- 1.9) times 10^{-10}cm^3 molecule^{-1}s ^{-1}. An upper limit for the heat of formation of IONO_2 of (21 +/- 3) kJmol^ {-1} was also derived. (Abstract shortened by UMI.).

  3. Electronic excitations by chemical reactions on metal surfaces

    NASA Astrophysics Data System (ADS)

    Nienhaus, Hermann

    2002-01-01

    Dissipation of chemical energy released in exothermic reactions at metal surfaces may happen adiabatically by creation of phonons or non-adiabatically by excitation of the electronic system of the metal or the reactants. In the past decades, the only direct experimental evidence for such non-adiabatic reactions has been exoelectron emission into vacuum and surface chemiluminescence which are observed in a special class of very exothermic reactions. The creation of e-h pairs in the metal has been discussed in many theoretical models but it was only recently that a novel experimental approach using Schottky diodes with ultrathin metal films makes direct measurement of reaction-induced hot electrons and holes possible. The chemical reaction creates hot charge carriers which travel ballistically from the metal film surface toward the Schottky interface and are detected as a chemicurrent in the diode. By now, such currents have been observed during adsorption of atomic hydrogen and deuterium on Ag, Cu and Fe surfaces as well as chemisorption of atomic and molecular oxygen, of NO and NO 2 molecules and of certain hydrocarbons on Ag. This paper reviews briefly exoelectron and chemiluminescence experiments and the concept of the Nrskov-Newns-Lundqvist model. The major part is devoted to the detection of chemically induced e-h pairs with thin metal film Si Schottky diodes by discussing the different influences on the chemicurrent magnitude and presenting experimental results predominantly with hydrogen and deuterium atoms. The experiments introduce a new method to investigate surface reaction kinetics and dynamics by use of an electronic device. In addition, the diodes may be used as selective reactive gas sensors.

  4. A Review of the Thermodynamic, Transport, and Chemical Reaction Rate Properties of High-temperature Air

    NASA Technical Reports Server (NTRS)

    Hansen, C Frederick; Heims, Steve P

    1958-01-01

    Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.

  5. Spatial patterns and double diffusion in chemical reactions

    PubMed Central

    Dewel, G.; Borckmans, P.; Walgraef, D.

    1983-01-01

    Spatial ordering has been observed recently during various photochemical reactions. Convoluted concentration bands first appear near the surface of shallow irradiated solutions. They thereafter extend into the bulk, and finger-like structures spontaneously develop. We discuss here the possible role of double-diffusion effects in the onset of this phenomenon. Indeed, chemical reactions occurring near the surface or evaporation of the solvent, or both, induce in the bulk adverse gradients of a pair of properties (concentrations of solute or concentration and temperature) having different diffusivities. This difference can then destabilize the homogeneous solution and trigger the observed patterns. PMID:16593384

  6. Tailoring oxidation degrees of graphene oxide by simple chemical reactions

    SciTech Connect

    Wang Gongkai; Sun Xiang; Lian Jie; Liu Changsheng

    2011-08-01

    High quality graphene oxide (GO) with controllable degrees of oxidation was synthesized by simple chemical reactions inspired by approaches to unzip single wall carbon nanotubes using strong oxidizing agents. As compared to the conventional Hummers method, these reactions are less exo-therm involved without emission of toxic gases. The structural characteristics of the synthesized GO with various oxidation degrees were evaluated by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, thermal gravimetric analysis, and UV-vis-IR spectroscopy. GO with tailored degrees of oxidation displays tunable optoelectronic properties and may have a significant impact on developing graphene- or GO-based platforms for various technological applications.

  7. Photochemical reactions of biologically important quinoxaline n-oxides

    SciTech Connect

    Dvoryantseva, G.G.; Tetenchuk, K.P.; Pol'shakov, V.I.; Elina, A.S.

    1987-02-01

    The authors study the photochemical reactions of quinoxidine, dioxidine, and a number of related derivatives of quinoxaline 1,4-di-N-oxides containing methyl, halomethyl, and carboxamide groups in the pyrazine ring. Thin-layer chromatography, UV spectrophotometry, and NMR/sup 1/H and /sup 13/C spectroscopy were used as the main methods for monitoring the photolysis process and establishing the structure of the products formed. The investigation established that two types of photochemical reactions are observed in the series of compounds discussed: photoisomerization with migration of a substitutent to the nitrogen atom of the heterocycle, and photorearrangement with elimination of a substituent and the formation of the corresponding lactams.

  8. Reaction kinetics of some important site-specific endonucleases.

    PubMed Central

    Hinsch, B; Kula, M R

    1981-01-01

    Reaction kinetics of the site-specific endonucleases BamHI, BgIII, C1aI, EcoRI, HpaII, PstI, SaII, SmaI, and XorII were investigated employing some frequently used substrates. Six of these enzymes could be analyzed under steady-state conditions. Kinetic data were obtained from progress curves applying an integrated Michaelis-Menten equation. KM ranged from 4 x 10(-9) M to 4 x 10(-11) M. Activities also spanned two orders of magnitude. In the case of C1aI the analysis of the pre-steady-state kinetics ("burst reaction") allowed the assessment of several rate constants. The rate-limiting step is the very slow dissociation of the enzyme-product complex (0.22 min(-1)). This complex is formed from the enzyme-bound nicked intermediate at a rate of 1.7 min(-1). The introduction of the first cut is again faster by a factor of about 6. SmaI and XorII resembled C1aI in their kinetics. The burst reaction can be used for the easy and unambiguous determination of molar concentrations of site-specific endonucleases in any preparation, which is free of non-specific DNases. PMID:6269074

  9. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    NASA Technical Reports Server (NTRS)

    Kinnison, Douglas E.; Wuebbles, Donald J.

    1994-01-01

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NO(x), Cl(x), HCl, N2O5, ClONO2 are calculated.

  10. Laser studies of chemical reaction and collision processes

    SciTech Connect

    Flynn, G.

    1993-12-01

    This work has concentrated on several interrelated projects in the area of laser photochemistry and photophysics which impinge on a variety of questions in combustion chemistry and general chemical kinetics. Infrared diode laser probes of the quenching of molecules with {open_quotes}chemically significant{close_quotes} amounts of energy in which the energy transferred to the quencher has, for the first time, been separated into its vibrational, rotational, and translational components. Probes of quantum state distributions and velocity profiles for atomic fragments produced in photodissociation reactions have been explored for iodine chloride.

  11. Finite element modeling of contaminant transport in soils including the effect of chemical reactions.

    PubMed

    Javadi, A A; Al-Najjar, M M

    2007-05-17

    The movement of chemicals through soils to the groundwater is a major cause of degradation of water resources. In many cases, serious human and stock health implications are associated with this form of pollution. Recent studies have shown that the current models and methods are not able to adequately describe the leaching of nutrients through soils, often underestimating the risk of groundwater contamination by surface-applied chemicals, and overestimating the concentration of resident solutes. Furthermore, the effect of chemical reactions on the fate and transport of contaminants is not included in many of the existing numerical models for contaminant transport. In this paper a numerical model is presented for simulation of the flow of water and air and contaminant transport through unsaturated soils with the main focus being on the effects of chemical reactions. The governing equations of miscible contaminant transport including advection, dispersion-diffusion and adsorption effects together with the effect of chemical reactions are presented. The mathematical framework and the numerical implementation of the model are described in detail. The model is validated by application to a number of test cases from the literature and is then applied to the simulation of a physical model test involving transport of contaminants in a block of soil with particular reference to the effects of chemical reactions. Comparison of the results of the numerical model with the experimental results shows that the model is capable of predicting the effects of chemical reactions with very high accuracy. The importance of consideration of the effects of chemical reactions is highlighted. PMID:17270344

  12. Potential for exothermic chemical reactions in waste tanks

    SciTech Connect

    Van Tuyl, H.H.

    1983-02-03

    The potential for exothermic chemical reactions in waste tanks at Hanford is discussed. Organic chemicals have been added to Hanford waste tanks, particularly as ferrocyanides and when processing sludges at B Plant. Recent planned or ongoing activities involving stored wastes have possibly increased the potential for reaction of these wastes with nitrate salts in the waste tanks. Risk evaluations appear to be deficient in assessing the consequences of a deflagration, and in determining the probability of either a deflagration or detonation. The present question is whether current plans and recent safety-related documentation have given proper consideration to the available information about organic compounds in waste tanks. The principal organic additions to Hanford waste tanks are 1200 tonnes of organic carbon'' and 500 tonnes of Ni{sub 2}Fe(CN){sub 6}. 13 refs.

  13. Implementation of a vibrationally linked chemical reaction model for DSMC

    NASA Technical Reports Server (NTRS)

    Carlson, A. B.; Bird, Graeme A.

    1994-01-01

    A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.

  14. Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product

    NASA Technical Reports Server (NTRS)

    David, Dennis D.; Dee, Louis A.; Beeson, Harold D.

    1997-01-01

    Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.

  15. Exploring chemical reaction mechanisms through harmonic Fourier beads path optimization

    NASA Astrophysics Data System (ADS)

    Khavrutskii, Ilja V.; Smith, Jason B.; Wallqvist, Anders

    2013-10-01

    Here, we apply the harmonic Fourier beads (HFB) path optimization method to study chemical reactions involving covalent bond breaking and forming on quantum mechanical (QM) and hybrid QM/molecular mechanical (QM/MM) potential energy surfaces. To improve efficiency of the path optimization on such computationally demanding potentials, we combined HFB with conjugate gradient (CG) optimization. The combined CG-HFB method was used to study two biologically relevant reactions, namely, L- to D-alanine amino acid inversion and alcohol acylation by amides. The optimized paths revealed several unexpected reaction steps in the gas phase. For example, on the B3LYP/6-31G(d,p) potential, we found that alanine inversion proceeded via previously unknown intermediates, 2-iminopropane-1,1-diol and 3-amino-3-methyloxiran-2-ol. The CG-HFB method accurately located transition states, aiding in the interpretation of complex reaction mechanisms. Thus, on the B3LYP/6-31G(d,p) potential, the gas phase activation barriers for the inversion and acylation reactions were 50.5 and 39.9 kcal/mol, respectively. These barriers determine the spontaneous loss of amino acid chirality and cleavage of peptide bonds in proteins. We conclude that the combined CG-HFB method further advances QM and QM/MM studies of reaction mechanisms.

  16. Stochastic Generator of Chemical Structure. 3. Reaction Network Generation

    SciTech Connect

    FAULON,JEAN-LOUP; SAULT,ALLEN G.

    2000-07-15

    A new method to generate chemical reaction network is proposed. The particularity of the method is that network generation and mechanism reduction are performed simultaneously using sampling techniques. Our method is tested for hydrocarbon thermal cracking. Results and theoretical arguments demonstrate that our method scales in polynomial time while other deterministic network generator scale in exponential time. This finding offers the possibility to investigate complex reacting systems such as those studied in petroleum refining and combustion.

  17. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, Frank P.; Herbst, Ronald S.

    1995-01-01

    The isotopes of boron, .sup.10 B and .sup.11 B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF.sub.3 and a liquid BF.sub.3 . donor molecular addition complex formed between BF.sub.3 gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone.

  18. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, F.P.; Herbst, R.S.

    1995-05-30

    The isotopes of boron, {sup 10}B and {sup 11}B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF{sub 3} and a liquid BF{sub 3} donor molecular addition complex formed between BF{sub 3} gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone. 1 Fig.

  19. Functional versus chemical diversity: is biodiversity important for drug discovery?

    PubMed

    Tulp, Martin; Bohlin, Lars

    2002-05-01

    Prospecting the full biodiversity of nature to find leads for new drugs is not necessary. Because finding leads is aimed at identifying biological activity, structure is of secondary importance. Furthermore, although natural chemical diversity might be unrivalled, functional diversity is bound to be considerably less. It is likely that many millions of chemically distinct molecules exist in nature but it is inconceivable that the number of different biological functions is near this number. This is corroborated by knowledge obtained from the genome sequences of an increasing number of species. It is unlikely that ligands for specific molecular targets are restricted to one species and even individual compounds are often found in more than one species. Important molecular mechanisms are likely to be ubiquitous and there are no a priori reasons to assume that some are restricted to, for example, tropical rainforests. Thus, there are no obvious advantages of "biodiversity prospecting", which will, possibly, endanger fragile ecosystems in the search for rare species. PMID:12008000

  20. Exploring complex chemical reactions by ab-initio simulation

    NASA Astrophysics Data System (ADS)

    Parrinello, Michele

    1998-03-01

    Recent progress in the ab-initio molecular dynamics method and the power of parallel computing, allow the detailed study of complex chemical reaction of great industrial relevance. We illustrate this unprecedented capability by investigating the second generation Ziegler-Natta catalytic process. In this inhomogeneous catalyst, a polymerization reaction is induced by TiCl4 molecules deposited on an MgCl2 solid support. A density functional based ab-initio molecular dynamics calculation conducted with a minimum of initial assumption allows to understand the nature of the catalytic center and to determine the reaction path with the associated free energy barrier. Furthermore our calculation can explain in a nontrivial way the stereo-selectivity of the process.

  1. Chemical reactions on metal oxide surfaces investigated by vibrational spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Yuemin; Wll, Christof

    2009-06-01

    The most successful method to unravel the microscopic mechanisms governing reactions in heterogeneous catalysis is the "surface science" approach which is based on well-controlled studies on model catalysts (usually single crystal surfaces) under ultrahigh vacuum (UHV) conditions [G. Ertl, Angew. Chem. 47 (2008) 3524]. In this review our recent vibrational spectroscopic studies on selected model reactions at various single-crystalline metal oxide surfaces are summarized. Two vibrational spectroscopic methods, high resolution electron energy loss spectroscopy (HREELS) and Fourier-transform infrared spectroscopy (FTIRS), were applied to characterize the adsorbed species and to elucidate the elementary processes of chemical reactions at oxide surfaces ranging from well-defined single crystals to modified surfaces with deliberately introduced defects. The combination of both methods allows us to extend the vibrational spectroscopic studies from ideal to complex systems.

  2. The nature of chemical reaction-driven tip-streaming

    NASA Astrophysics Data System (ADS)

    Mayer, H. C.; Krechetnikov, R.

    2013-05-01

    The discovery of chemical reaction-driven tip-streaming (also known as "an amazing drop") was made about a decade ago during measurements of the dynamic interfacial tension of a water-alkali pendant droplet immersed in oil-linoleic acid. A plausible explanation for this self-sustained ejection of micron sized droplets from the tip of the macroscopic pendant drop was offered at that time and attributed to Marangoni stresses driving the reaction-produced surfactant along the interface. Later, asymptotic theory based on the analysis of a complete fluid dynamical formulation supported this hypothesis. As this discovery promised a way of microdroplet generation without the need for complex microchannel geometries or externally imposed flow or electric fields, we were recently motivated to study the influence of the reagent concentrations and reaction rate on the droplet generation. However, in an attempt to recreate the original experiments, we revealed that the cause for tip-streaming is not what it originally seemed to be. This led to a series of experiments clarifying the role of the Marangoni stresses and the crucial differences from similar phenomena. As the mechanism by which the phenomenon was originally thought to operate was supported by recent theoretical studies, the present work leads to new intriguing questions of existence and conditions under which a chemical reaction alone can drive Marangoni stresses capable of self-sustaining the process of tip-streaming.

  3. Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods.

    PubMed

    Suleimanov, Yury V; Green, William H

    2015-09-01

    We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation double- and single-ended transition-state optimization algorithms-the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several single-molecule systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only "known" reaction pathways, manually detected in the previous studies, but also new, previously "unknown", reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes. PMID:26575920

  4. Chemical reactions studied at ultra-low temperature in liquid helium clusters

    NASA Astrophysics Data System (ADS)

    Huisken, Friedrich; Krasnokutski, Serge A.

    2012-11-01

    Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope 4He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O2. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

  5. Chemical reactions studied at ultra-low temperature in liquid helium clusters

    SciTech Connect

    Huisken, Friedrich; Krasnokutski, Serge A.

    2012-11-27

    Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope {sup 4}He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O{sub 2}. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

  6. Production of cold formaldehyde molecules for study and control of chemical reaction.

    SciTech Connect

    Taatjes, Craig A.; Bochinski, J. R.; Bohn, John L.; Ye, Jun; Lewandowski, H. J.; Sawyer, Brian C.; Ticknor, Christopher; Hudson, Eric R.

    2005-08-01

    We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H{sub 2}CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of H{sub 2}CO. We have decelerated a molecular beam of H{sub 2}CO essentially to rest, producing molecules at 100 mK with a density of {approx} 10{sup 6} cm{sup -3}.

  7. Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals

    SciTech Connect

    Hudson, Eric R.; Ticknor, Christopher; Sawyer, Brian C.; Taatjes, Craig A.; Lewandowski, H. J.; Bochinski, J. R.; Bohn, J. L.; Ye Jun

    2006-06-15

    We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H{sub 2}CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of H{sub 2}CO. We have decelerated a molecular beam of H{sub 2}CO essentially to rest, producing molecules at 100 mK with a density of {approx}10{sup 6} cm{sup -3}.

  8. Chemical dynamics in the gas phase: Time-dependent quantum mechanics of chemical reactions

    SciTech Connect

    Gray, S.K.

    1993-12-01

    A major goal of this research is to obtain an understanding of the molecular reaction dynamics of three and four atom chemical reactions using numerically accurate quantum dynamics. This work involves: (i) the development and/or improvement of accurate quantum mechanical methods for the calculation and analysis of the properties of chemical reactions (e.g., rate constants and product distributions), and (ii) the determination of accurate dynamical results for selected chemical systems, which allow one to compare directly with experiment, determine the reliability of the underlying potential energy surfaces, and test the validity of approximate theories. This research emphasizes the use of recently developed time-dependent quantum mechanical methods, i.e. wave packet methods.

  9. Mesoscale simulations of shockwave energy dissipation via chemical reactions

    NASA Astrophysics Data System (ADS)

    Antillon, Edwin; Strachan, Alejandro

    2015-06-01

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials under shockwave-loading conditions. An additional implicit variable (the particle size) is used to describe volume-reducing chemical reactions using an intra-molecular potential inspired by Transition State Theory, while the dynamics of the center-of-mass motion evolves according to inter-particle forces. The equations of motion are derived from a Hamiltonian and the model captures both: total energy conservation and Galilean invariance. We demonstrate that this model captures complex thermo-mechanical-chemical processes, and we use these features to explore materials with the capabilities to dissipate shocks-wave energy due to ballistic impacts. Our results characterize how the parameters of the chemical model affect shock-wave attenuation, and we elucidate on how the coupling between the different energy-transferring mechanisms influences nucleation of chemistry for conditions away from equilibrium.

  10. [Recent results in research on oscillatory chemical reactions].

    PubMed

    Poros, Eszter; Kurin-Csrgei, Krisztina

    2014-01-01

    The mechanisms of the complicated periodical phenomenas in the nature (e.g. hearth beat, sleep cycle, circadian rhythms, etc) could be understood with using the laws of nonlinear chemical systems. In this article the newest result in the research of the subfield of nonlinear chemical dynamics aimed at constructing oscillatory chemical reactions, which are novel either in composition or in configuration, are presented. In the introductory part the concept of chemical periodicity is defined, then the forms as it can appear in time and space and the methods of their study are discussed. Detailed description of the experimental work that has resulted in two significant discoveries is provided. A method was developed to design pH-oscillators which are capable of operating under close conditions. The batch pH-oscillators are more convenient to use in some proposed applications than the equivalent CSTR variant. A redox oscillator that is new in composition was found. The permanganate oxidation of some amino acids was shown to take place according to oscillatory kinetics in a narrow range of the experimental parameters. The KMnO4 - glycine - Na2HPO4 system represents the first example in the family of manganese based oscillators where amino acids is involved. In the conclusion formal analogies between the simple chemical and some more complicated biological oscillatory phenomena are mentioned and the possibility of modeling periodic processes with the use of information gained from the studies of chemical oscillations is pointed out. PMID:25872277

  11. Chemical reaction dynamics using the Advanced Light Source

    SciTech Connect

    Yang, X.; Blank, D.A.; Heimann, P.A.; Lee, Y.T.; Suits, A.G. |; Lin, J.; Wodtke, A.M.

    1995-09-01

    The recently commissioned Advanced Light Source (ALS) at Berkeley provides a high brightness, tunable VUV light source for chemical dynamics studies. A dedicated chemical dynamics beamline has been built at the ALS for studies of fundamental chemical processes. High flux (10{sup 16} photon/s with 2% bandwidth) VUV synchrotron radiation from 5 to 30 eV can be obtained from the beamline, whose source is the U8/10 undulator. Three endstations will be in operation for studies ranging from crossed beam reaction dynamics and photodissociation to high resolution photoionization dynamics and spectroscopy. A rotatable source crossed molecular beam apparatus (endstation one) has been established for unimolecular and bimolecular reactive scattering studies. Photodissociation of methylamine and ozone were carried out using VUV synchrotron radiation as the ionization detection technique at this endstation. Results show the advantages of the new endstation using VUV ionization as the detection scheme over similar machines using electron bombardment as the ionization source.

  12. Computational Analyses of Complex Flows with Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Bae, Kang-Sik

    The heat and mass transfer phenomena in micro-scale for the mass transfer phenomena on drug in cylindrical matrix system, the simulation of oxygen/drug diffusion in a three dimensional capillary network, and a reduced chemical kinetic modeling of gas turbine combustion for Jet propellant-10 have been studied numerically. For the numerical analysis of the mass transfer phenomena on drug in cylindrical matrix system, the governing equations are derived from the cylindrical matrix systems, Krogh cylinder model, which modeling system is comprised of a capillary to a surrounding cylinder tissue along with the arterial distance to veins. ADI (Alternative Direction Implicit) scheme and Thomas algorithm are applied to solve the nonlinear partial differential equations (PDEs). This study shows that the important factors which have an effect on the drug penetration depth to the tissue are the mass diffusivity and the consumption of relevant species during the time allowed for diffusion to the brain tissue. Also, a computational fluid dynamics (CFD) model has been developed to simulate the blood flow and oxygen/drug diffusion in a three dimensional capillary network, which are satisfied in the physiological range of a typical capillary. A three dimensional geometry has been constructed to replicate the one studied by Secomb et al. (2000), and the computational framework features a non-Newtonian viscosity model for blood, the oxygen transport model including in oxygen-hemoglobin dissociation and wall flux due to tissue absorption, as well as an ability to study the diffusion of drugs and other materials in the capillary streams. Finally, a chemical kinetic mechanism of JP-10 has been compiled and validated for a wide range of combustion regimes, covering pressures of 1atm to 40atm with temperature ranges of 1,200 K--1,700 K, which is being studied as a possible Jet propellant for the Pulse Detonation Engine (PDE) and other high-speed flight applications such as hypersonic missiles. The comprehensive skeletal mechanism consists of 58 species and 315 reactions including in CPD, Benzene formation process by the theory for polycyclic aromatic hydrocarbons (PAH) and soot formation process on the constant volume combustor, premixed flame characteristics.

  13. Isotope and vibrational excitation effects in ultracold chemical reactions

    NASA Astrophysics Data System (ADS)

    Pradhan, Gagan B.; Balakrishnan, N.; Kendrick, Brian K.

    2014-05-01

    We discuss the effect of vibrational excitation on chemical reaction between O(1 D) and H2 and OH+O at cold and ultracold temperatures. The effect of isotope substitution is investigated by exploring dynamics of O(1 D)+D2 reaction and comparing results against its H2 counterpart. It is found that while vibrational excitation has a moderate effect on OH+O reaction, it has only marginal effect on O(1 D)+H2/D2 reactions. For v = 2 and v = 3 of OH it is found that non-reactive relaxation pathway is dominated by a multi quantum process than a sequential single quantum pathway. Kinetic isotope effect is determined for the O(1 D)+H2/D2 systems as the ratio of rate coefficients for H2 and D2 reactions and comparisons are made with available room temperature experimental data. This work was supported in part by NSF grant PHY-1205838 (N.B.) and ARO MURI grant No. W911NF-12-1-0476.

  14. APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

    Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

  15. APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

    Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

  16. Chemical reactions occurring during direct solar reduction of CO2.

    PubMed

    Lyma, J L; Jensen, R J

    2001-09-28

    At high temperatures carbon dioxide may absorb solar radiation and react to form carbon monoxide and molecular oxygen. The CO, so produced, may be converted by well-established means to a combustible fuel, such as methanol. We intend to make a future demonstration of the solar reduction of CO2 based on these processes. This paper, however, addresses only the problem of preserving, or even enhancing, the initial photolytic CO by quenching the hot gas with colder H2O or CO2. We present model calculations with a reaction mechanism used extensively in other calculations. If a CO2 gas stream is heated and photolyzed by intense solar radiation and then allowed to cool slowly, it will react back to the initial CO2 by a series of elementary chemical reactions. The back reaction to CO2 can be terminated with the rapid addition of CO2, water, or a mixture. Calculations show that a three-fold quench with pure CO2 will stop the reactions and preserve over 90% of the initial photolytic CO. We find that water has one of two effects. It can either increase the CO level, or it can catalyze the recombination of O and CO to CO2. The gas temperature is the determining factor. If the quench gas is not sufficient to keep the temperature below approximately 1100 K, a chain-branching reaction dominates and the reaction to CO2 occurs. If the temperature stays below that level a chain terminating reaction dominates and the CO is increased. The former case occurs below approximately a fourfold quench with a water/CO2 mixture. The later case occurs when the quench is greater than fourfold. We conclude that CO2, H2O, or a mixture may quench the hot gas stream photolyzed by solar radiation and preserve the photolytic CO. PMID:11589409

  17. Chemical and mechanical feedback during reaction rim growth

    NASA Astrophysics Data System (ADS)

    Milke, R.; Tajcmanova, L.

    2012-12-01

    The system MgO-SiO2, including the mineral reaction quadruple periclase-forsterite-enstatite-quartz, has for several years become a favored target for laboratory and thought experiments on reaction rim growth, on the possible grain-scale pressure variability evolving during metamorphic reactions, and on the role of the local reaction volume in guiding kinetic pathways. Both isotope tracer and microstructure analyses indicate that the relative opposite fluxes of MgO and SiO2 components obey the limitations in space dictated by the stoichiometry of the local partial reactions. However, if the component's mobility is high, this implies local competition between mineral growth and the yield strength of the surrounding matrix, thus local pressure variation. Experimentally this is validated by the significant differences in Opx rim thickness, either forming around Ol in Qtz matrix, or around Qtz in Ol matrix, in one and the same experiment. Tantamount observations have been experimentally made in the CaO-SiO2 and CaO-MgO-SiO2 systems. In all these laboratory experiments, the presence of traces of water has been identified as a leading variable controlling the mobility of chemical species. Trace amounts of water follow local pressure gradients and speed up reaction rates where local volume change is negative. New results indicate that at least in coarse grained rocks, total water contents in the 10 ppm range might increase chemical fluxes along grain boundaries by orders of magnitude. The majority of metamorphic rocks in the Earth's crust is dominated by aluminuous silicates and quartz. Reaction rims in aluminosilicate lithologies have been studied in samples of high-pressure felsic granulites from the Bohemian Massif (Variscan belt of Central Europe). They show well developed plagioclase reaction rims around kyanite grains in two microstructural settings. Plagioclase rims around kyanite inclusions within large perthites have a radial thickness of up to 50 ?m, whereas the radial thickness of plagioclase rims around kyanites in the polycrystalline matrix is significantly larger, up to 200 ?m. The difference in the rim thickness for the two microstructural settings is ascribed to the complex interplay of the efficiency of chemical mass transfer and the mechanical response of the surrounding matrix next to the reaction site. Our data based on numerical modelling show that the microstructure may be generated and maintained on the geological time scale as a result of the mechanical feedback induced by the local reactions taking place in restricted space. In general, the observations from experimental and natural systems indicate that assumed equilibria in metamorphic rocks must be generally considered as local equilibria. This includes not only the chemical composition of metamorphic minerals, but also the strength of the surrounding matrix in which they form.

  18. [Anaphylactic reactions to low-molecular weight chemicals].

    PubMed

    Nowak, Daria; Panaszek, Bernard

    2015-01-01

    Low-molecular weight chemicals (haptens) include a large group of chemical compounds occurring in work environment, items of everyday use (cleaning products, clothing, footwear, gloves, furniture), jewelry (earrings, bracelets), drugs, especially in cosmetics. They cause type IV hypersensitive reactions. During the induction phase of delayed-type hypersensitivity, haptens form complexes with skin proteins. After internalization through antigen presenting cells, they are bound to MHC class II molecules. Next, they are exposed against specific T-lymphocytes, what triggers activation of Th1 cells mainly. After repeating exposition to that hapten, during effector phase, Th1 induce production of cytokines affecting non-specific inflammatory cells. Usually, it causes contact dermatitis. However, occasionally incidence of immediate generalized reactions after contact with some kinds of haptens is noticed. A question arises, how the hapten does induce symptoms which are typical for anaphylaxis, and what contributes to amplification of this mechanism. It seems that this phenomenon arises from pathomechanism occurring in contact urticaria syndrome in which an anaphylactic reaction may be caused either by contact of sensitized skin with protein antigens, high-molecular weight allergens, or haptens. One of the hypotheses indicates the leading role of basophiles in this process. Their contact with haptens, may cause to release mediators of immediate allergic reaction (histamine, eicosanoids) and to produce cytokines corresponding to Th2 cells profile. Furthermore, Th17 lymphocytes secreting pro-inflammatory interleukin-17 might be engaged into amplifying hypersensitivity into immediate reactions and regulatory T-cells may play role in the process, due to insufficient control of the activity of effector cells. PMID:25661919

  19. Chemical reaction network approaches to Biochemical Systems Theory.

    PubMed

    Arceo, Carlene Perpetua P; Jose, Editha C; Marin-Sanguino, Alberto; Mendoza, Eduardo R

    2015-11-01

    This paper provides a framework to represent a Biochemical Systems Theory (BST) model (in either GMA or S-system form) as a chemical reaction network with power law kinetics. Using this representation, some basic properties and the application of recent results of Chemical Reaction Network Theory regarding steady states of such systems are shown. In particular, Injectivity Theory, including network concordance [36] and the Jacobian Determinant Criterion [43], a "Lifting Theorem" for steady states [26] and the comprehensive results of Mller and Regensburger [31] on complex balanced equilibria are discussed. A partial extension of a recent Emulation Theorem of Cardelli for mass action systems [3] is derived for a subclass of power law kinetic systems. However, it is also shown that the GMA and S-system models of human purine metabolism [10] do not display the reactant-determined kinetics assumed by Mller and Regensburger and hence only a subset of BST models can be handled with their approach. Moreover, since the reaction networks underlying many BST models are not weakly reversible, results for non-complex balanced equilibria are also needed. PMID:26363083

  20. The influence of overlap interactions on chemical reactions in confinement

    NASA Astrophysics Data System (ADS)

    Santiso, Erik E.; Gubbins, Keith E.; George, Aaron M.; Buongiorno Nardelli, Marco

    2007-03-01

    Chemical reactions are often carried out in nano-structured materials due to their large surface area per unit mass. It is, however, difficult to understand fully the role of the nano-structure in many reactions due to the superposition of multiple effects. Such effects include: the reduced dimensionality of the system, the heterogeneity of the pore surfaces, the selective adsorption of reactants/products, catalytic effects, and transport limitations. Experimental studies often show many of these effects at the same time, making the results difficult to interpret. In this work we present results of density functional theory calculations illustrating the influence of overlap interactions (shape-catalytic effects) on chemical reactions. In particular, we show the effect of confinement in small pores on the rates of rotational isomerizations of n-butane, 1-butene and 1,3-butadiene. We find that the rates of these transitions change as the double exponential of the pore size in the molecular sieving limit. These results are a first step towards an integrated model for the design of catalytic materials.

  1. Holistic Metrics for Assessment of the Greenness of Chemical Reactions in the Context of Chemical Education

    ERIC Educational Resources Information Center

    Ribeiro, M. Gabriela T. C.; Machado, Adelio A. S. C.

    2013-01-01

    Two new semiquantitative green chemistry metrics, the green circle and the green matrix, have been developed for quick assessment of the greenness of a chemical reaction or process, even without performing the experiment from a protocol if enough detail is provided in it. The evaluation is based on the 12 principles of green chemistry. The

  2. Holistic Metrics for Assessment of the Greenness of Chemical Reactions in the Context of Chemical Education

    ERIC Educational Resources Information Center

    Ribeiro, M. Gabriela T. C.; Machado, Adelio A. S. C.

    2013-01-01

    Two new semiquantitative green chemistry metrics, the green circle and the green matrix, have been developed for quick assessment of the greenness of a chemical reaction or process, even without performing the experiment from a protocol if enough detail is provided in it. The evaluation is based on the 12 principles of green chemistry. The…

  3. Characterization of plastic deformation and chemical reaction in titanium-polytetrafluoroethylene mixture

    NASA Astrophysics Data System (ADS)

    Davis, Jeffery Jon

    1998-09-01

    The subject of this dissertation is the deformation process of a single metal - polymer system (titanium - polytetrafluoroethylene) and how this process leads to initiation of chemical reaction. Several different kinds of experiments were performed to characterize the behavior of this material to shock and impact. These mechanical conditions induce a rapid plastic deformation of the sample. All of the samples tested had an initial porosity which increased the plastic flow condition. It is currently believed that during the deformation process two important conditions occur: removal of the oxide layer from the metal and decomposition of the polymer. These conditions allow for rapid chemical reaction. The research from this dissertation has provided insight into the complex behavior of plastic deformation and chemical reactions in titanium - polytetrafluoroethylene (PTFE, Teflon). A hydrodynamic computational code was used to model the plastic flow for correlation with the results from the experiments. The results from this work are being used to develop an ignition and growth model for metal/polymer systems. Three sets of experiments were used to examine deformation of the 80% Ti and 20% Teflon materials: drop- weight, gas gun, and split-Hopkinson pressure bar. Recovery studies included post shot analysis of the samples using x-ray diffraction. Lagrangian hydrocode DYNA2D modeling of the drop-weight tests was performed for comparison with experiments. One of the reactions know to occur is Ti + C ? TiC (s) which results in an exothermic release. However, the believed initial reactions occur between Ti and fluorine which produces TixFy gases. The thermochemical code CHEETAH was used to investigate the detonation products and concentrations possible during Ti - Teflon reaction. CHEETAH shows that the Ti - fluorine reactions are thermodynamically favorable. This research represents the most comprehensive to date study of deformation induced chemical reaction in metal/polymers.

  4. A quantum informational approach for dissecting chemical reactions

    NASA Astrophysics Data System (ADS)

    Duperrouzel, Corinne; Tecmer, Pawe?; Boguslawski, Katharina; Barcza, Gergely; Legeza, rs; Ayers, Paul W.

    2015-02-01

    We present a conceptionally different approach to dissect bond-formation processes in metal-driven catalysis using concepts from quantum information theory. Our method uses the entanglement and correlation among molecular orbitals to analyze changes in electronic structure that accompany chemical processes. As a proof-of-principle example, the evolution of nickel-ethene bond-formation is dissected, which allows us to monitor the interplay of back-bonding and ?-donation along the reaction coordinate. Furthermore, the reaction pathway of nickel-ethene complexation is analyzed using quantum chemistry methods, revealing the presence of a transition state. Our study supports the crucial role of metal-to-ligand back-donation in the bond-forming process of nickel-ethene.

  5. Chemical characteristics of mineral trioxide aggregate and its hydration reaction

    PubMed Central

    2012-01-01

    Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed. PMID:23429542

  6. Thermal energy storage. [by means of chemical reactions

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.

    1975-01-01

    The principles involved in thermal energy storage by sensible heat, chemical potential energy, and latent heat of fusion are examined for the purpose of evolving selection criteria for material candidates in the low ( 0 C) and high ( 100 C) temperature ranges. The examination identifies some unresolved theoretical considerations and permits a preliminary formulation of an energy storage theory. A number of candidates in the low and high temperature ranges are presented along with a rating of candidates or potential candidates. A few interesting candidates in the 0 to 100 C region are also included. It is concluded that storage by means of reactions whose reversibility can be controlled either by product removal or by catalytic means appear to offer appreciable advantages over storage with reactions whose reversability cannot be controlled. Among such advantages are listed higher heat storage capacities and more favorable options regarding temperatures of collection, storage, and delivery. Among the disadvantages are lower storage efficiencies.

  7. Nature of the chemical reaction for furfural modified asphalt

    SciTech Connect

    Memon, G.M.; Chollar, B.H.

    1994-12-31

    Three of the most serious problems of asphalt pavements today are rutting, cracking, and susceptibility to moisture damage (stripping). Asphalt manufacturers have been mixing asphalts with polymers to produce polymer-modified asphalts with improved rheological properties. However, the costs for these improved polymer-modified asphalts are almost double that of regular asphalts. FHWA researchers have found that asphalt modified by the chemical, furfural (which is prepared by simple elimination reaction of aldopentoses obtained from oat hulls), exhibited better stripping properties and was less temperature susceptible than the virgin asphalt while costing less than polymer-modified asphalts. This paper discusses the possible structure of the furfural-modified asphalt, data for the virgin and furfural-modified asphalts and their Corbett fractions, data from a model reaction between phenol and furfural, and a possible explanation of this structure based on these data.

  8. Chemical characteristics of mineral trioxide aggregate and its hydration reaction.

    PubMed

    Chang, Seok-Woo

    2012-11-01

    Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed. PMID:23429542

  9. Transient assembly of active materials fueled by a chemical reaction.

    PubMed

    Boekhoven, Job; Hendriksen, Wouter E; Koper, Ger J M; Eelkema, Rienk; van Esch, Jan H

    2015-09-01

    Fuel-driven self-assembly of actin filaments and microtubules is a key component of cellular organization. Continuous energy supply maintains these transient biomolecular assemblies far from thermodynamic equilibrium, unlike typical synthetic systems that spontaneously assemble at thermodynamic equilibrium. Here, we report the transient self-assembly of synthetic molecules into active materials, driven by the consumption of a chemical fuel. In these materials, reaction rates and fuel levels, instead of equilibrium composition, determine properties such as lifetime, stiffness, and self-regeneration capability. Fibers exhibit strongly nonlinear behavior including stochastic collapse and simultaneous growth and shrinkage, reminiscent of microtubule dynamics. PMID:26339025

  10. Transient assembly of active materials fueled by a chemical reaction

    NASA Astrophysics Data System (ADS)

    Boekhoven, Job; Hendriksen, Wouter E.; Koper, Ger J. M.; Eelkema, Rienk; van Esch, Jan H.

    2015-09-01

    Fuel-driven self-assembly of actin filaments and microtubules is a key component of cellular organization. Continuous energy supply maintains these transient biomolecular assemblies far from thermodynamic equilibrium, unlike typical synthetic systems that spontaneously assemble at thermodynamic equilibrium. Here, we report the transient self-assembly of synthetic molecules into active materials, driven by the consumption of a chemical fuel. In these materials, reaction rates and fuel levels, instead of equilibrium composition, determine properties such as lifetime, stiffness, and self-regeneration capability. Fibers exhibit strongly nonlinear behavior including stochastic collapse and simultaneous growth and shrinkage, reminiscent of microtubule dynamics.

  11. Structural cluster analysis of chemical reactions in solution

    NASA Astrophysics Data System (ADS)

    Gallet, Grgoire A.; Pietrucci, Fabio

    2013-08-01

    We introduce a simple and general approach to the problem of clustering structures from atomic trajectories of chemical reactions in solution. By considering distance metrics which are invariant under permutation of identical atoms or molecules, we demonstrate that it is possible to automatically resolve as distinct structural clusters the configurations corresponding to reactants, products, and transition states, even in presence of atom-exchanges and of hundreds of solvent molecules. Our approach strongly simplifies the analysis of large trajectories and it opens the way to the construction of kinetic network models of activated processes in solution employing the available efficient schemes developed for proteins conformational ensembles.

  12. Method for detecting pollutants. [through chemical reactions and heat treatment

    NASA Technical Reports Server (NTRS)

    Rogowski, R. S.; Richards, R. R.; Conway, E. J. (Inventor)

    1976-01-01

    A method is described for detecting and measuring trace amounts of pollutants of the group consisting of ozone, nitrogen dioxide, and carbon monoxide in a gaseous environment. A sample organic solid material that will undergo a chemical reaction with the test pollutant is exposed to the test environment and thereafter, when heated in the temperature range of 100-200 C., undergoes chemiluminescence that is measured and recorded as a function of concentration of the test pollutant. The chemiluminescence of the solid organic material is specific to the pollutant being tested.

  13. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  14. On the chemical reaction of matter with antimatter.

    PubMed

    Lodi Rizzini, Evandro; Venturelli, Luca; Zurlo, Nicola

    2007-06-01

    A chemical reaction between the building block antiatomic nucleus, the antiproton (p or H- in chemical notation), and the hydrogen molecular ion (H2+) has been observed by the ATHENA collaboration at CERN. The charged pair interact via the long-range Coulomb force in the environment of a Penning trap which is purpose-built to observe antiproton interactions. The net result of the very low energy collision of the pair is the creation of an antiproton-proton bound state, known as protonium (Pn), together with the liberation of a hydrogen atom. The Pn is formed in a highly excited, metastable, state with a lifetime against annihilation of around 1 micros. Effects are observed related to the temperature of the H2+ prior to the interaction, and this is discussed herein. PMID:17492700

  15. Peptide Bond Synthesis by a Mechanism Involving an Enzymatic Reaction and a Subsequent Chemical Reaction.

    PubMed

    Abe, Tomoko; Hashimoto, Yoshiteru; Zhuang, Ye; Ge, Yin; Kumano, Takuto; Kobayashi, Michihiko

    2016-01-22

    We recently reported that an amide bond is unexpectedly formed by an acyl-CoA synthetase (which catalyzes the formation of a carbon-sulfur bond) when a suitable acid and l-cysteine are used as substrates. DltA, which is homologous to the adenylation domain of nonribosomal peptide synthetase, belongs to the same superfamily of adenylate-forming enzymes, which includes many kinds of enzymes, including the acyl-CoA synthetases. Here, we demonstrate that DltA synthesizes not only N-(d-alanyl)-l-cysteine (a dipeptide) but also various oligopeptides. We propose that this enzyme catalyzes peptide synthesis by the following unprecedented mechanism: (i) the formation of S-acyl-l-cysteine as an intermediate via its "enzymatic activity" and (ii) subsequent "chemical" S ? N acyl transfer in the intermediate, resulting in peptide formation. Step ii is identical to the corresponding reaction in native chemical ligation, a method of chemical peptide synthesis, whereas step i is not. To the best of our knowledge, our discovery of this peptide synthesis mechanism involving an enzymatic reaction and a subsequent chemical reaction is the first such one to be reported. This new process yields peptides without the use of a thioesterified fragment, which is required in native chemical ligation. Together with these findings, the same mechanism-dependent formation of N-acyl compounds by other members of the above-mentioned superfamily demonstrated that all members most likely form peptide/amide compounds by using this novel mechanism. Each member enzyme acts on a specific substrate; thus, not only the corresponding peptides but also new types of amide compounds can be formed. PMID:26586916

  16. Importance of toxicokinetics for interspecies variation in sensitivity to chemicals.

    PubMed

    Nyman, Anna-Maija; Schirmer, Kristin; Ashauer, Roman

    2014-05-20

    Interspecies variation in sensitivity to synthetic chemicals can be orders of magnitude large. Species traits causing the variation can be related to toxicokinetics (uptake, distribution, biotransformation, elimination) or toxicodynamics (interaction with biological target sites). We present an approach to systematically measure and model the contribution of uptake, biotransformation, internal distribution, and elimination kinetics toward species sensitivity differences. The aim is to express sensitivity as target tissue specific, internal lethal concentrations. A case study with the pesticides diazinon, imidacloprid, and propiconazole and the aquatic invertebrates Gammarus pulex, Gammarus fossarum, and Lymnaea stagnalis illustrates the approach. L. stagnalis accumulates more pesticides than Gammaridae when measured in whole organisms but less in target tissues such as the nervous system. Toxicokinetics, i.e. biotransformation and distribution, explain the higher tolerance of L. stagnalis to the insecticide diazinon when compared to Gammaridae. L. stagnalis was again more tolerant to the other neurotoxicant imidacloprid; however, the difference in sensitivity could not be explained by toxicokinetics alone, indicating the importance of toxicodynamic differences. Sensitivity to propiconazole was comparable among all species and, when expressed as internal lethal concentrations, falls in the range of baseline toxicity. PMID:24758734

  17. Two-scale large deviations for chemical reaction kinetics through second quantization path integral

    NASA Astrophysics Data System (ADS)

    Li, Tiejun; Lin, Feng

    2016-04-01

    Motivated by the study of rare events for a typical genetic switching model in systems biology, in this paper we aim to establish the general two-scale large deviations for chemical reaction systems. We build a formal approach to explicitly obtain the large deviation rate functionals for the considered two-scale processes based upon the second quantization path integral technique. We get three important types of large deviation results when the underlying two timescales are in three different regimes. This is realized by singular perturbation analysis to the rate functionals obtained by the path integral. We find that the three regimes possess the same deterministic mean-field limit but completely different chemical Langevin approximations. The obtained results are natural extensions of the classical large volume limit for chemical reactions. We also discuss its implication on the single-molecule Michaelis–Menten kinetics. Our framework and results can be applied to understand general multi-scale systems including diffusion processes.

  18. Flow Tube Studies of Gas Phase Chemical Processes of Atmospheric Importance

    NASA Technical Reports Server (NTRS)

    Molina, Mario J.

    1998-01-01

    The objective of this project is to conduct measurements of elementary reaction rate constants and photochemical parameters for processes of importance in the atmosphere. These measurements are being carried out under temperature and pressure conditions covering those applicable to the stratosphere and upper troposphere, using the chemical ionization mass spectrometry turbulent flow technique developed in our laboratory. The next section summarizes our research activities during the first year of the project, and the section that follows consists of the statement of work for the third year. Additional details concerning the projects listed in the statement of work were described in our original proposal.

  19. Machine learning of chemical reactivity from databases of organic reactions.

    PubMed

    Carrera, Gonçalo V S M; Gupta, Sunil; Aires-de-Sousa, João

    2009-07-01

    Databases of chemical reactions contain knowledge about the reactivity of specific reagents. Although information is in general only explicitly available for compounds reported to react, it is possible to derive information about substructures that do not react in the reported reactions. Both types of information (positive and negative) can be used to train machine learning techniques to predict if a compound reacts or not with a specific reagent. The whole process was implemented with two databases of reactions, one involving BuNH2 as the reagent, and the other NaCNBH3. Negative information was derived using MOLMAP molecular descriptors, and classification models were developed with Random Forests also based on MOLMAP descriptors. MOLMAP descriptors were based exclusively on calculated physicochemical features of molecules. Correct predictions were achieved for approximately 90% of independent test sets. While NaCNBH3 is a selective reducing reagent widely used in organic synthesis, BuNH2 is a nucleophile that mimics the reactivity of the lysine side chain (involved in an initiating step of the mechanism leading to skin sensitization). PMID:19468693

  20. Computational organic chemistry: bridging theory and experiment in establishing the mechanisms of chemical reactions.

    PubMed

    Cheng, Gui-Juan; Zhang, Xinhao; Chung, Lung Wa; Xu, Liping; Wu, Yun-Dong

    2015-02-11

    Understanding the mechanisms of chemical reactions, especially catalysis, has been an important and active area of computational organic chemistry, and close collaborations between experimentalists and theorists represent a growing trend. This Perspective provides examples of such productive collaborations. The understanding of various reaction mechanisms and the insight gained from these studies are emphasized. The applications of various experimental techniques in elucidation of reaction details as well as the development of various computational techniques to meet the demand of emerging synthetic methods, e.g., C-H activation, organocatalysis, and single electron transfer, are presented along with some conventional developments of mechanistic aspects. Examples of applications are selected to demonstrate the advantages and limitations of these techniques. Some challenges in the mechanistic studies and predictions of reactions are also analyzed. PMID:25568962

  1. Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells

    NASA Technical Reports Server (NTRS)

    Hansen, Lee D.; Frank, Harvey

    1987-01-01

    Work is described that was designed to determine the kinetic constants necessary to extrapolate kinetic data on Li/SOCl2 cells over the temperature range from 25 to 75 C. A second objective was to characterize as far as possible the chemical reactions that occur in the cells since these reactions may be important in understanding the potential hazards of these cells. The kinetics of the corrosion processes in undischarged Li/SOCl2 cells were determined and separated according to their occurrence at the anode and cathode; the effects that switching the current on and off has on the corrosion reactions was determined; and the effects of discharge state on the kinetics of the corrosion process were found. A thermodynamic analysis of the current-producing reactions in the cell was done and is included.

  2. Review and analysis of high temperature chemical reactions and the effect of non-equilibrium conditions

    NASA Technical Reports Server (NTRS)

    Johnson, R. E.

    1986-01-01

    Chemical reactions at high temperatures have been considered extensively because of their importance to the heating effects on re-entry of space vehicles. Data on these reactions however, are not abundant and even when found there are discrepancies in data collected by various investigators. In particular, data for recombination reactions are calculated from the dissociation reactions or vice versa through the equilibrium constant. This involves the use of the principle of detailed balancing. This principle is discussed in reference to conditions where it is valid as well as to those where it is not valid. Related topics that merit further study or for which applicable information was available are briefly mentioned in an appendix to this report.

  3. THE IMPORTANCE OF SPATIAL ACCURACY FOR CHEMICAL INFORMATION MANAGEMENT

    EPA Science Inventory

    Information about chemicals can be critical to making timely decisions. The results of these decisions may not be realized for many years. In order to increase the value of chemical information and to create and utilize meaningful environmental models, the Environmental Prote...

  4. The quantum dynamics of electronically nonadiabatic chemical reactions

    NASA Technical Reports Server (NTRS)

    Truhlar, Donald G.

    1993-01-01

    Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally adiabatic functions in various quantum scattering algorithms.

  5. Computed Potential Energy Surfaces and Minimum Energy Pathway for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

    1994-01-01

    Computed potential energy surfaces are often required for computation of such observables as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method with the Dunning correlation consistent basis sets to obtain accurate energetics, gives useful results for a number of chemically important systems. Applications to complex reactions leading to NO and soot formation in hydrocarbon combustion are discussed.

  6. Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2010-06-01

    A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  7. Laboratory Studies of Homogeneous and Heterogeneous Chemical Processes of Importance in the Upper Atmosphere

    NASA Technical Reports Server (NTRS)

    Molina, Mario J.

    2001-01-01

    The objective of this study is to conduct measurements of chemical kinetics parameters for reactions of importance in the stratosphere and upper troposphere, and to study the interaction of trace gases such as HCl with ice surfaces in order to elucidate the mechanism of heterogeneous chlorine activation processes, using both a theoretical and an experimental approach. The measurements will be carried out under temperature and pressure conditions covering those applicable to the stratosphere and upper troposphere. The techniques to be employed include turbulent flow - chemical ionization mass spectrometry, and optical ellipsometry. The next section summarizes our research activities during the second year of the project, and the section that follows consists of the statement of work for the third year.

  8. Does capillarity influence chemical reaction in drops and bubbles? A thermodynamic approach.

    PubMed

    Sanfeld, A; Sefiane, K; Benielli, D; Steinchen, A

    2000-07-28

    After a brief introduction on the variables which describe the physico-chemical properties of a fluid surface, this paper compares, in a very simple way, the equilibrium constant of homogeneous and heterogeneous reactions taking place in spherical micro-objects (uncharged and charged droplets and bubbles) and in media bordered by a flat interface. This quantity is by definition the exponential of the dimensionless standard chemical affinity whose values (< or = 0, > or = 0) may indicate the direction and the importance of the reaction (strictly true when the mixing term of the affinity is zero). The classical thermodynamic approach combined with the Laplace equation shows that: (i) high surface tension and high curvature influence the equilibrium constant, this effect being, however, much more important for bubbles than for droplets; (ii) charges on droplets reduce this effect; (iii) the constant of reaction taking place in the vapour in contact with a charged droplet depends significantly on the electric field pressure; (iv) reactions in droplets dispersed in the liquid phase are discussed and, in particular, capillarity seems to play a negligible role on reactions in micro-emulsions; (v) the surface amount of a gas bubble component transferred in the continuous liquid can be related to capillary quantities; (vi) expanding (or shrinking) bubble induced by a chemical reaction is analysed by using an extended Laplace law which includes the volumetric flow rate; (vii) the Laplace law is discussed in the frame of the choice of the dividing surface. Numerous actual examples from the atmosphere, sonochemistry and metallurgy illustrate the theory proposed. One of the interest, among other points, is that small objects (specially bubbles) give the potentiality to obtain, for steady or (near) equilibrium states, large amount of components which would not be possible when dealing with large reservoirs. PMID:10997763

  9. Chemical Reactions in the Processing of Mosi2 + Carbon Compacts

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Lee, Kang N.; Maloy, Stuart A.; Heuer, Arthur H.

    1993-01-01

    Hot-pressing of MoSi2 powders with carbon at high temperatures reduces the siliceous grain boundary phase in the resultant compact. The chemical reactions in this process were examined using the Knudsen cell technique. A 2.3 wt pct oxygen MoSi2 powder and a 0.59 wt pct oxygen MoSi2 powder, both with additions of 2 wt pct carbon, were examined. The reduction of the siliceous grain boundary phase was examined at 1350 K and the resultant P(SiO)/P(CO) ratios interpreted in terms of the SiO(g) and CO(g) isobars on the Si-C-O predominance diagram. The MoSi2 + carbon mixtures were then heated at the hot-pressing temperature of 2100 K. Large weight losses were observed and could be correlated with the formation of a low-melting eutectic and the formation and vaporization of SiC.

  10. Luminescence from Collapsing Centimeter Bubbles Expanded by Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Duplat, Jrme; Villermaux, Emmanuel

    2015-08-01

    We report on a new method for realizing an exceptionally strong inertial confinement of a gas in a liquid: A centimetric spherical bubble filled with a reactive gaseous mixture in a liquid is expanded by an exothermic chemical reaction whose products condense in the liquid at the bubble wall. Hence, the cavity formed in this way is essentially empty as it collapses. The temperatures reached at maximum compression, inferred from the cavity radius dynamics and further confirmed by spectroscopic measurements exceed 20 000 K. Because the cavity is typically big, our findings also provide unique space and time resolved sequences of the events accompanying the collapse, notably the development of the inertial instability notoriously known to deter strong compression.

  11. Waste Heat Recovery from Blast Furnace Slag by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Qin, Yuelin; Lv, Xuewei; Bai, Chenguang; Qiu, Guibao; Chen, Pan

    2012-08-01

    Blast furnace (BF) slag, which is the main byproduct in the ironmaking process, contains large amounts of sensible heat. To recover the heat, a new waste heat-recovery systemgranulating molten BF slag by rotary multinozzles cup atomizer and pyrolyzing printed circuited board with obtained hot BF slag particlewas proposed in this study. The feasibility of the waste heat-recovery system was verified by dry granulation and pyrolyzation experiments. The energy of hot BF slag could be converted to chemical energy through the pyrolysis reaction, and a large amount of combustible gas like CO, H2, C m H n , and CH4 can be generated during the process.

  12. Modeling chemical reactions in laser-induced plasmas

    NASA Astrophysics Data System (ADS)

    Shabanov, S. V.; Gornushkin, I. B.

    2015-11-01

    Under the assumption of local thermal equilibrium, a numerical algorithm is proposed to find the equation of state for laser-induced plasmas (LIPs) in which chemical reactions are permitted in addition to ionization processes. The Coulomb interaction in plasma is accounted for by the Debye-Hckel method. The algorithm is used to calculate the equation of state for LIPs containing carbon, silicon, nitrogen, and argon. The equilibrium reaction constants are calculated using the latest experimental and ab initio data of spectroscopic constants for the molecules {N}_2, {C}_2, {Si}_2, {CN}, {SiN}, {SiC} and their ions. The algorithm is incorporated into a fluid dynamic numerical model based on the Navier-Stokes equations describing an expansion of LIP plumes into an ambient gas. The dynamics of LIP plumes obtained by the ablation of SiC, solid silicon, or solid carbon in an ambient gas containing {N}_2 and Ar is simulated to study formation of molecules and molecular ions.

  13. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Ziaul Huque

    2007-08-31

    This is the final technical report for the project titled 'Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks'. The aim of the project was to develop an efficient chemistry model for combustion simulations. The reduced chemistry model was developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) was used via a new network topology known as Non-linear Principal Components Analysis (NPCA). A commonly used Multilayer Perceptron Neural Network (MLP-NN) was modified to implement NPCA-NN. The training rate of NPCA-NN was improved with the GEneralized Regression Neural Network (GRNN) based on kernel smoothing techniques. Kernel smoothing provides a simple way of finding structure in data set without the imposition of a parametric model. The trajectory data of the reaction mechanism was generated based on the optimization techniques of genetic algorithm (GA). The NPCA-NN algorithm was then used for the reduction of Dimethyl Ether (DME) mechanism. DME is a recently discovered fuel made from natural gas, (and other feedstock such as coal, biomass, and urban wastes) which can be used in compression ignition engines as a substitute for diesel. An in-house two-dimensional Computational Fluid Dynamics (CFD) code was developed based on Meshfree technique and time marching solution algorithm. The project also provided valuable research experience to two graduate students.

  14. Modeling of Sheath Ion-Molecule Reactions in Plasma Enhanced Chemical Vapor Deposition of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Hash, David B.; Govindan, T. R.; Meyyappan, M.

    2004-01-01

    In many plasma simulations, ion-molecule reactions are modeled using ion energy independent reaction rate coefficients that are taken from low temperature selected-ion flow tube experiments. Only exothermic or nearly thermoneutral reactions are considered. This is appropriate for plasma applications such as high-density plasma sources in which sheaths are collisionless and ion temperatures 111 the bulk p!asma do not deviate significantly from the gas temperature. However, for applications at high pressure and large sheath voltages, this assumption does not hold as the sheaths are collisional and ions gain significant energy in the sheaths from Joule heating. Ion temperatures and thus reaction rates vary significantly across the discharge, and endothermic reactions become important in the sheaths. One such application is plasma enhanced chemical vapor deposition of carbon nanotubes in which dc discharges are struck at pressures between 1-20 Torr with applied voltages in the range of 500-700 V. The present work investigates The importance of the inclusion of ion energy dependent ion-molecule reaction rates and the role of collision induced dissociation in generating radicals from the feedstock used in carbon nanotube growth.

  15. Site remediation via Dispersion by Chemical Reaction (DCR). Special report

    SciTech Connect

    Marion, G.M.; Payne, J.R.; Brar, G.S.

    1997-08-01

    The DCR (Dispersion by Chemical Reaction) technologies are a group of patented waste treatment processes using CaO (quicklime) for the immobilization of heavily oiled sludges, oil-contaminated soils, acid-tars, and heavy metals in Ca(OH)2 and CaCO3 matrices. The objectives of this project were to: (1) evaluate the DCR process for remediating soils contaminated with pesticides, petroleum hydrocarbons (oils and fuels), and heavy metals in cold regions and (2) evaluate DCR-treated oil-contaminated soil as a non-frost-susceptible (NFS) construction material. Three major studies evaluated the DCR process to remediate (1) hydrocarbons at Eareckson Air Force Station on Shemya in the Aleutians, (2) pesticide-contaminated soils from Rocky Mt. Arsenal, and (3) heavy-metal contaminated soils from a former zinc smelter site at Palmerton, Pennsylvania. The DCR process was successful in stabilizing liquid organics and heavy metals in contaminated soils. The chemical properties of soils contaminated by solid organics (asphalt tar and pesticides) were not generally improved by the DCR process, but even in these cases, the physical properties were improved for potential reuse as construction materials.

  16. Oparin's coacervates as an important milestone in chemical evolution

    NASA Astrophysics Data System (ADS)

    Kolb, Vera M.

    2015-09-01

    Although Oparin's coacervate model for the origin of life by chemical evolution is almost 100 years old, it is still valid. However, the structure of his originally proposed coacervate is not considered prebiotic, based on some recent developments in prebiotic chemistry. We have remedied this deficiency of the Oparin's model, by substituting his coacervate with a prebiotically feasible one. Oparin's coacervates are aqueous structures, but have a boundary with the rest of the aqueous medium. They exhibit properties of self-replication, and provide a path to a primitive metabolism, via chemical competition and thus a primitive selection. Thus, coacervates are good models for proto-cells. We review here some salient points of Oparin's model and address also some philosophical views on the beginning of natural selection in primitive chemical systems.

  17. Chemical reactions of excited nitrogen atoms for short wavelength chemical lasers. Final technical report

    SciTech Connect

    Not Available

    1989-12-15

    Accomplishments of this program include the following: (1) Scalable, chemical generation of oxygen atoms by reaction of fluorine atoms and water vapor. (2) Production of nitrogen atom densities of 1 {times} 10{sup 1}5 cm{sup {minus}3} with 5% electrical efficiency by injecting trace amounts of fluorine into microwave discharged nitrogen. (3) Production of cyanide radicals by reaction of high densities of N atoms with cyanogen. (4) Production of carbon atoms by reaction of nitrogen atoms with cyanogen or with fluorine atoms and hydrogen cyanide. (5) Confirmation that the reaction of carbon atoms and carbonyl sulfide produces CS(a{sup 3} {Pi}{sub r}), as predicted by conservation of electron spin and orbital angular momenta and as proposed by others under another SWCL program. (6) Production of cyanide radicals by injection of cyanogen halides into active nitrogen and use as spectroscopic calibration source. (7) Demonstration that sodium atoms react with cyanogen chloride, bromide and iodide and with cyanuric trifluoride to produce cyanide radicals. (8) Demonstration of the potential utility of the fluorine atom plus ammonia reaction system in the production of NF(b{sup l}{Sigma}{sup +}) via N({sup 2}D) + F{sub 2}.

  18. Chemical Reaction and Flow Modeling in Fullerene and Nanotube Production

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.; Farhat, Samir; Greendyke, Robert B.

    2004-01-01

    The development of processes to produce fullerenes and carbon nanotubes has largely been empirical. Fullerenes were first discovered in the soot produced by laser ablation of graphite [1]and then in the soot of electric arc evaporated carbon. Techniques and conditions for producing larger and larger quantities of fullerenes depended mainly on trial and error empirical variations of these processes, with attempts to scale them up by using larger electrodes and targets and higher power. Various concepts of how fullerenes and carbon nanotubes were formed were put forth, but very little was done based on chemical kinetics of the reactions. This was mainly due to the complex mixture of species and complex nature of conditions in the reactors. Temperatures in the reactors varied from several thousand degrees Kelvin down to near room temperature. There are hundreds of species possible, ranging from atomic carbon to large clusters of carbonaceous soot, and metallic catalyst atoms to metal clusters, to complexes of metals and carbon. Most of the chemical kinetics of the reactions and the thermodynamic properties of clusters and complexes have only been approximated. In addition, flow conditions in the reactors are transient or unsteady, and three dimensional, with steep spatial gradients of temperature and species concentrations. All these factors make computational simulations of reactors very complex and challenging. This article addresses the development of the chemical reaction involved in fullerene production and extends this to production of carbon nanotubes by the laser ablation/oven process and by the electric arc evaporation process. In addition, the high-pressure carbon monoxide (HiPco) process is discussed. The article is in several parts. The first one addresses the thermochemical aspects of modeling; and considers the development of chemical rate equations, estimates of reaction rates, and thermodynamic properties where they are available. The second part addresses modeling of the arc process for fullerene and carbon nanotube production using O-D, 1-D and 2-D fluid flow models. The third part addresses simulations of the pulsed laser ablation process using time-dependent techniques in 2-D, and a steady state 2-D simulation of a continuous laser ablation process. The fourth part addresses steady state modeling in O-D and 2-D of the HiPco process. In each of the simulations, there is a variety of simplifications that are made that enable one to concentrate on one aspect or another of the process. There are simplifications that can be made to the chemical reaction models , e.g. reduction in number of species by lumping some of them together in a representative species. Other simulations are carried out by eliminating the chemistry altogether in order to concentrate on the fluid dynamics. When solving problems with a large number of species in more than one spatial dimension, it is almost imperative that the problem be decoupled by solving for the fluid dynamics to find the fluid motion and temperature history of "particles" of fluid moving through a reactor. Then one can solve the chemical rate equations with complex chemistry following the temperature and pressure history. One difficulty is that often mixing with an ambient gas is involved. Therefore, one needs to take dilution and mixing into account. This changes the ratio of carbon species to background gas. Commercially available codes may have no provision for including dilution as part of the input. One must the write special solvers for including dilution in decoupled problems. The article addresses both ful1erene production and single-walled carbon nanotube (SWNT) production. There are at least two schemes or concepts of SWNT growth. This article will only address growth in the gas phase by carbon and catalyst cluster growth and SW T formation by the addition of carbon. There are other models that conceive of SWNT growth as a phase separation process from clusters me up carbon and metal catalyst, with the carbon precipitating from the cluster as it cools. We will not deal with that concept in this article. Further research is needed to determine the rates at which these composite clusters form, evaporate, and segregate.

  19. Coupling of hydrologic transport and chemical reactions in a stream affected by acid mine drainage

    USGS Publications Warehouse

    Kimball, B.A.; Broshears, R.E.; Bencala, K.E.; McKnight, Diane M.

    1994-01-01

    Experiments in St. Kevin Gulch, an acid mine drainage stream, examined the coupling of hydrologic transport to chemical reactions affecting metal concentrations. Injection of LiCl as a conservative tracer was used to determine discharge and residence time along a 1497-m reach. Transport of metals downstream from inflows of acidic, metal-rich water was evaluated based on synoptic samples of metal concentrations and the hydrologic characteristics of the stream. Transport of SO4 and Mn was generally conservative, but in the subreaches most affected by acidic inflows, transport was reactive. Both 0.1-??m filtered and particulate Fe were reactive over most of the stream reach. Filtered Al partitioned to the particulate phase in response to high instream concentrations. Simulations that accounted for the removal of SO4, Mn, Fe, and Al with first-order reactions reproduced the steady-state profiles. The calculated rate constants for net removal used in the simulations embody several processes that occur on a stream-reach scale. The comparison between rates of hydrologie transport and chemical reactions indicates that reactions are only important over short distances in the stream near the acidic inflows, where reactions occur on a comparable time scale with hydrologic transport and thus affect metal concentrations.

  20. The Theory of Thermodynamics for Chemical Reactions in Dispersed Heterogeneous Systems

    PubMed

    Yongqiang; Baojiao; Jianfeng

    1997-07-01

    In this paper, the expressions of Gibbs energy change, enthalpy change, entropy change, and equilibrium constant for chemical reactions in dispersed heterogeneous systems are derived using classical thermodynamics theory. The thermodynamical relations for the same reaction system between the dispersed and the block state are also derived. The effects of degree of dispersion on thermodynamical properties, reaction directions, and chemical equilibria are discussed. The results show that the present equation of thermodynamics for chemical reactions is only a special case of the above-mentioned formulas and that the effect of the dispersity of a heterogeneous system on the chemical reaction obeys the Le Chatelier principle of movement of equilibria. PMID:9241206

  1. Progression in High School Students' (Aged 16-18) Conceptualizations about Chemical Reactions in Solution.

    ERIC Educational Resources Information Center

    Boo, Hong-Kwen; Watson, J. R.

    2001-01-01

    Explores the development over time of students' understandings of the concept of chemical reaction in the context of two familiar reactions in solution. Based on interviews (n=48), results show that students made some progress in their understanding of the concept of chemical reaction but some fundamental misconceptions remained. (Author/MM)

  2. CH 1 Introduction to Chemistry. Study Guide to Minicourse I - 13 Chemical Reaction Principles.

    ERIC Educational Resources Information Center

    Schlenker, Richard

    Provided is a study guide for an introductory minicourse to the principles of chemical reactions. This written text is designed to accompany a series of audio tapes and 35mm slides which the student studies at his own pace. The course presents chemical kinetics, reaction mechanisms, reaction rates, and equilibrium. (SL)

  3. No electron left behind: a rule-based expert system to predict chemical reactions and reaction mechanisms

    PubMed Central

    Chen, Jonathan H.; Baldi, Pierre

    2009-01-01

    Predicting the course and major products of arbitrary reactions is a fundamental problem in chemistry, one that chemists must address in a variety of tasks ranging from synthesis design to reaction discovery. Described here is an expert system to predict organic chemical reactions based on a knowledge base of over 1,500 manually composed reaction transformation rules. Novel rule extensions are introduced to enable robust predictions and describe detailed reaction mechanisms at the level of electron flows in elementary reaction steps, ensuring that all reactions are properly balanced and atom-mapped. The core reaction prediction functionalities of this expert system are illustrated with applications including: (1) prediction of detailed reaction mechanisms; (2) computer-based learning in organic chemistry; (3) retro synthetic analysis; and (4) combinatorial library design. Select applications available via http://cdb.ics.uci.edu. PMID:19719121

  4. Chemical dynamics in the gas phase : quantum mechanics of chemical reactions.

    SciTech Connect

    Gray, S. K.

    2006-01-01

    This research program focuses on both the development and application of accurate quantum mechanical methods to describe gas phase chemical reactions and highly excited molecules. Emphasis is often placed on time-dependent or integrative approaches that, in addition to computational simplifications, yield useful mechanistic insights. Applications to systems of current experimental and theoretical interest are emphasized. The results of these calculations also allow one to gauge the quality of the underlying potential energy surfaces and the reliability of more approximate theoretical approaches such as classical trajectories and transition state theories.

  5. Chemical Characterization of Secondary Organic Aerosol Formed from Atmospheric Aqueous-phase Reactions of Phenolic Compounds

    NASA Astrophysics Data System (ADS)

    Yu, L.; Smith, J.; Anastasio, C.; Zhang, Q.

    2012-12-01

    Phenolic compounds, which are released in significant amounts from biomass burning, may undergo fast aqueous-phase reactions to form secondary organic aerosol (SOA) in the atmosphere. Understanding the aqueous-phase reaction mechanisms of these compounds and the composition of their reaction products is thus important for constraining SOA sources and predicting organic aerosol properties in models. In this study, we investigate the aqueous-phase reactions of three phenols (phenol, guaiacol and syringol) with two oxidants - excited triplet states (3C*) of non-phenolic aromatic carbonyls and hydroxyl radical (OH). By employing four analytical methods including high-resolution aerosol mass spectrometry, total organic carbon analysis, ion chromatography, and liquid chromatography-mass spectrometry, we thoroughly characterize the chemical compositions of the low volatility reaction products of phenols and propose formation mechanisms based on this information. Our results indicate that phenolic SOA is highly oxygenated, with O/C ratios in the range of 0.83-1.03, and that the SOA of phenol is usually more oxidized than those of guaiacol and syringol. Among the three precursors, syringol generates the largest fraction of higher molecular weight (MW) products. For the same precursor, the SOA formed via reaction with 3C* is less oxidized than that formed via reaction with OH. In addition, oxidation by 3C* enhances the formation of higher MW species, including phenolic dimers, higher oligomers and hydroxylated products, compared to reactions initiated by OH, which appear to favor the formation of organic acids. However, our results indicate that the yields of small organic acids (e.g., formate, acetate, oxalate, and malate) are low for both reaction pathways, together accounting for less than 5% of total SOA mass.

  6. Numerical solutions of several reflected shock-wave flow fields with nonequilibrium chemical reactions

    NASA Technical Reports Server (NTRS)

    Hanson, R. K.; Presley, L. L.; Williams, E. V.

    1972-01-01

    The method of characteristics for a chemically reacting gas is used in the construction of the time-dependent, one-dimensional flow field resulting from the normal reflection of an incident shock wave at the end wall of a shock tube. Nonequilibrium chemical reactions are allowed behind both the incident and reflected shock waves. All the solutions are evaluated for oxygen, but the results are generally representative of any inviscid, nonconducting, and nonradiating diatomic gas. The solutions clearly show that: (1) both the incident- and reflected-shock chemical relaxation times are important in governing the time to attain steady state thermodynamic properties; and (2) adjacent to the end wall, an excess-entropy layer develops wherein the steady state values of all the thermodynamic variables except pressure differ significantly from their corresponding Rankine-Hugoniot equilibrium values.

  7. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2005-12-01

    This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a novel procedure to speed up the training of NPCA. The same procedure termed L{sub 2}Boost can be used to increase the order of approximation of the Generalized Regression Neural Network (GRNN). It is pointed out that GRNN is a basic procedure for the emerging mesh free CFD. Also reported is an efficient simple approach of computing the derivatives of GRNN function approximation using complex variables or the Complex Step Method (CSM). The results presented demonstrate the significance of the methods developed and will be useful in many areas of applied science and engineering.

  8. Heat Diffusion in Gases, Including Effects of Chemical Reaction

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick

    1960-01-01

    The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.

  9. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2004-12-01

    This is an annual technical report for the work done over the last year (period ending 9/30/2004) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a procedure to speed up the training of NPCA. The developed procedure is based on the non-parametric statistical technique of kernel smoothing. When this smoothing technique is implemented as a Neural Network, It is know as Generalized Regression Neural Network (GRNN). We present results of implementing GRNN on a test problem. In addition, we present results of an in house developed 2-D CFD code that will be used through out the project period.

  10. Using a Natural Analogue to Investigate Chemical Reactions Associated with Carbon Dioxide Sequestration

    NASA Astrophysics Data System (ADS)

    Navarre-Sitchler, A.; Kaszuba, J.; Thyne, G.

    2008-12-01

    Capture and storage of carbon dioxide in deep underground geologic formations (geologic carbon sequestration) is currently the most advanced technology for reducing or mitigating anthropogenic carbon dioxide emissions. There are a number of scientific challenges associated with injection and storage of large amounts of CO2 in geologic formations. Understanding the chemical reactions that can occur among reservoir rocks, aqueous fluids, and supercritical carbon dioxide other gasses is one of these challenges. Natural analogues to CO2 sequestration are systems where carbon dioxide has been stored over geologic time scales. By studying these analogues we can determine important chemical reactions between the host rock and stored gases. The Moxa Arch is a structural feature located in the southern end of the greater Green River Basin, Wyoming. Carbon dioxide and methane were emplaced in Paleozoic rocks, including the 1000 feet thick Mississippian age Madison Limestone, of the Moxa Arch through natural processes. Concentrations of carbon dioxide in the emplaced gas in these formations vary in the region of the Moxa Arch from 70-95% and are as low as ~ 15% in gas producing areas outside of the Moxa Arch. Methane, hydrogen sulfide and helium comprise the balance of the gas compositons. Geochemical reaction path and reactive transport models based upon the mineralogy of 12 core samples collected from three wells completed in the Madison Limestone near the Moxa Arch will be presented. These models help identify potential geochemical reactions between reservoir minerals and stored gasses.

  11. Massively parallel computation of 3D flow and reactions in chemical vapor deposition reactors

    SciTech Connect

    Salinger, A.G.; Shadid, J.N.; Hutchinson, S.A.; Hennigan, G.L.; Devine, K.D.; Moffat, H.K.

    1997-12-01

    Computer modeling of Chemical Vapor Deposition (CVD) reactors can greatly aid in the understanding, design, and optimization of these complex systems. Modeling is particularly attractive in these systems since the costs of experimentally evaluating many design alternatives can be prohibitively expensive, time consuming, and even dangerous, when working with toxic chemicals like Arsine (AsH{sub 3}): until now, predictive modeling has not been possible for most systems since the behavior is three-dimensional and governed by complex reaction mechanisms. In addition, CVD reactors often exhibit large thermal gradients, large changes in physical properties over regions of the domain, and significant thermal diffusion for gas mixtures with widely varying molecular weights. As a result, significant simplifications in the models have been made which erode the accuracy of the models` predictions. In this paper, the authors will demonstrate how the vast computational resources of massively parallel computers can be exploited to make possible the analysis of models that include coupled fluid flow and detailed chemistry in three-dimensional domains. For the most part, models have either simplified the reaction mechanisms and concentrated on the fluid flow, or have simplified the fluid flow and concentrated on rigorous reactions. An important CVD research thrust has been in detailed modeling of fluid flow and heat transfer in the reactor vessel, treating transport and reaction of chemical species either very simply or as a totally decoupled problem. Using the analogy between heat transfer and mass transfer, and the fact that deposition is often diffusion limited, much can be learned from these calculations; however, the effects of thermal diffusion, the change in physical properties with composition, and the incorporation of surface reaction mechanisms are not included in this model, nor can transitions to three-dimensional flows be detected.

  12. Chemical reactions on rutile TiO2(110).

    PubMed

    Lun Pang, Chi; Lindsay, Robert; Thornton, Geoff

    2008-10-01

    Understanding the surface chemistry of TiO2 is key to the development and optimisation of many technologies, such as solar power, catalysis, gas sensing, medical implantation, and corrosion protection. In order to address this, considerable research effort has been directed at model single crystal surfaces of TiO2. Particular attention has been given to the rutile TiO2(110) surface because it is the most stable face of TiO2. In this critical review, we discuss the chemical reactivity of TiO2(110), focusing in detail on four molecules/classes of molecules. The selected molecules are water, oxygen, carboxylic acids, and alcohols-all of which have importance not only to industry but also in nature (173 references). PMID:18818830

  13. Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kabbani, Mohamad A.; Tiwary, Chandra Sekhar; Autreto, Pedro A. S.; Brunetto, Gustavo; Som, Anirban; Krishnadas, K. R.; Ozden, Sehmus; Hackenberg, Ken P.; Gong, Yongi; Galvao, Douglas S.; Vajtai, Robert; Kabbani, Ahmad T.; Pradeep, Thalappil; Ajayan, Pulickel M.

    2015-06-01

    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.

  14. Evaluation of reaction mechanism of coal-metal oxide interactions in chemical-looping combustion

    SciTech Connect

    Siriwardane, Ranjani; Richards, George; Poston, James; Tian, Hanjing; Miller, Duane; Simonyi, Thomas

    2010-11-15

    The knowledge of reaction mechanism is very important in designing reactors for chemical-looping combustion (CLC) of coal. Recent CLC studies have considered the more technically difficult problem of reactions between abundant solid fuels (i.e. coal and waste streams) and solid metal oxides. A definitive reaction mechanism has not been reported for CLC reaction of solid fuels. It has often been assumed that the solid/solid reaction is slow and therefore requires that reactions be conducted at temperatures high enough to gasify the solid fuel, or decompose the metal oxide. In contrast, data presented in this paper demonstrates that solid/solid reactions can be completed at much lower temperatures, with rates that are technically useful as long as adequate fuel/metal oxide contact is achieved. Density functional theory (DFT) simulations as well as experimental techniques such as thermo-gravimetric analysis (TGA), flow reactor studies, in situ X-ray photo electron spectroscopy (XPS), in situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to evaluate how the proximal interaction between solid phases proceeds. The data indicate that carbon induces the Cu-O bond breaking process to initiate the combustion of carbon at temperatures significantly lower than the spontaneous decomposition temperature of CuO, and the type of reducing medium in the vicinity of the metal oxide influences the temperature at which the oxygen release from the metal oxide takes place. Surface melting of Cu and wetting of carbon may contribute to the solid-solid contacts necessary for the reaction. (author)

  15. Computational molecular technology towards macroscopic chemical phenomena-molecular control of complex chemical reactions, stereospecificity and aggregate structures

    NASA Astrophysics Data System (ADS)

    Nagaoka, Masataka

    2015-12-01

    A new efficient hybrid Monte Carlo (MC)/molecular dynamics (MD) reaction method with a rare event-driving mechanism is introduced as a practical `atomistic' molecular simulation of large-scale chemically reactive systems. Starting its demonstrative application to the racemization reaction of (R)-2-chlorobutane in N,N-dimethylformamide solution, several other applications are shown from the practical viewpoint of molecular controlling of complex chemical reactions, stereochemistry and aggregate structures. Finally, I would like to mention the future applications of the hybrid MC/MD reaction method.

  16. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2006-09-21

    This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the significant development made in developing a truly meshfree computational fluid dynamics (CFD) flow solver to be coupled to NPCA. First, the procedure of obtaining nearly analytic accurate first order derivatives using the complex step method (CSM) is extended to include computation of accurate meshfree second order derivatives via a theorem described in this report. Next, boosted generalized regression neural network (BGRNN), described in our previous report is combined with CSM and used to obtain complete solution of a hard to solve wave dominated sample second order partial differential equation (PDE): the cubic Schrodinger equation. The resulting algorithm is a significant improvement of the meshfree technique of smooth particle hydrodynamics method (SPH). It is suggested that the demonstrated meshfree technique be termed boosted smooth particle hydrodynamics method (BSPH). Some of the advantages of BSPH over other meshfree methods include; it is of higher order accuracy than SPH; compared to other meshfree methods, it is completely meshfree and does not require any background meshes; It does not involve any construction of shape function with their associated solution of possibly ill conditioned matrix equations; compared to some SPH techniques, no equation for the smoothing parameter is required; finally it is easy to program.

  17. New Measurements of the Astrophysically Important ^44Ti Radionuclide Through the ^40Ca(?,?)^44Ti Reaction

    NASA Astrophysics Data System (ADS)

    Robertson, Daniel; Becker, Hans-Werner; Collon, Philippe; Goerres, Joachim; Wiescher, Michael

    2010-11-01

    The relatively short-lived radionuclide ^44Ti (t1/2=58.9 0.3 yrs), is of considerable importance in the study of nucleosynthesis in explosive stellar environments. It's production predominantly through the ^40Ca(?,?)^44Ti reaction, takes place during ?-rich freeze-out, in the inner most layers of a core-collapse supernova. A number of experimental studies have been previously performed to determine the stellar reaction rate. These studies included prompt ?-ray measurements from in-beam experiments, atom counting techniques utilizing accelerator mass spectrometry (AMS) and multi energy step measurements at the DRAGON recoil mass separator. The resulting calculated reaction rates show drastic disagreement. New results from experiments at the DTL, Bochum and NSL, Notre Dame, used both gamma spectroscopy and AMS techniques to measure the reaction, and investigate the discrepancies in both the experimental and predicted results. Final results of the experiments and their impact on the reaction rate will be discussed.

  18. Measurements and analysis of alpha-induced reactions of importance for nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    de Messieres, Genevieve Escande

    2011-11-01

    Reactions during stellar helium burning are of primary importance for understanding nucleosynthesis. A detailed understanding of the critical reaction chain 4He(2alpha, gamma)12C( alpha, gamma)16O(alpha, gamma) 20Ne is necessary both because it is the primary energy source and because it determines the ratio of 12C to 16O produced, which in turn significantly effects subsequent nucleosynthesis. Also during Helium burning, the reactions 22Ne(alpha, n)25Mg and 22Ne(alpha, gamma )26Mg are crucial in determining the amount of neutrons available for the astrophysical s-process. This thesis presents new experimental results concerning the 16O(alpha, gamma) 20Ne, 22Ne(alpha, n)25Mg, and 22Ne(alpha, gamma)26Mg reaction rates. These results are then applied to the calculation of the associated stellar reaction rates in order to achieve better accuracy.

  19. Multiscale modelling on the shock-induced chemical reactions of multifunctional energetic structural materials

    NASA Astrophysics Data System (ADS)

    Qiao, L.; Zhang, X. F.; He, Y.; Zhao, X. N.; Guan, Z. W.

    2013-05-01

    Multifunctional energetic structural materials (MESMs) are usually granular mixtures, which release energy due to exothermic chemical reaction initiated under shock loading conditions. The mesostructure, in terms of the size, shape, and distribution of granular mixture, plays a significant role in chemical reaction and the energy release characteristics of MESMs. However, it is difficult to model such a complex process involving thermal-mechanical-chemical responses, especially the effects of the initial mesostructures. In this paper, a multiscale modelling approach is proposed to simulate the chemical reaction of MESMs under a shock compression. The thermal-mechanical response of MESMs is first obtained from mesoscale simulations. Then, the macroscale thermochemical model for a shock-induced chemical reaction is given, in which the extent of reaction is considered. Finally, the spatial profiles of temperature and pressure from the mesoscale heterogeneous simulation are homogenized into cells as an initial state for chemical reaction and further combined with the thermochemical model in macroscale. Hence this provides insight into thermal-mechanical-chemical responses based on the initial mesostructures. Aluminum/Tungsten/Polytetrafluoroethylene granular mixture is selected to demonstrate the method and the effects of volume fraction and impact velocity on the shock-induced chemical reaction. The multiscale approach developed, which combines the mesoscale simulation and macroscale thermochemical modelling, can be used to predict the shock-induced chemical reaction of MESMs with different mesoscale characteristics over a wide range of impact velocities.

  20. Probing Isotope Effects in Chemical Reactions Using Single Ions

    NASA Astrophysics Data System (ADS)

    Staanum, Peter F.; Hjbjerre, Klaus; Wester, Roland; Drewsen, Michael

    2008-06-01

    Isotope effects in reactions between Mg+ in the 3p P3/22 excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only 250 reactions with HD, the branching ratio between formation of MgD+ and MgH+ is found to be larger than 5. From an additional 65 reactions with H2 and D2 we find that the overall fragmentation probability of the intermediate MgH2+, MgHD+, or MgD2+ complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.

  1. Computed Potential Energy Surfaces and Minimum Energy Pathways for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

    1994-01-01

    Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. For some dynamics methods, global potential energy surfaces are required. In this case, it is necessary to obtain the energy at a complete sampling of all the possible arrangements of the nuclei, which are energetically accessible, and then a fitting function must be obtained to interpolate between the computed points. In other cases, characterization of the stationary points and the reaction pathway connecting them is sufficient. These properties may be readily obtained using analytical derivative methods. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives usefull results for a number of chemically important systems. The talk will focus on a number of applications including global potential energy surfaces, H + O2, H + N2, O(3p) + H2, and reaction pathways for complex reactions, including reactions leading to NO and soot formation in hydrocarbon combustion.

  2. Sum over Histories Representation for Kinetic Sensitivity Analysis: How Chemical Pathways Change When Reaction Rate Coefficients Are Varied.

    PubMed

    Bai, Shirong; Davis, Michael J; Skodje, Rex T

    2015-11-12

    The sensitivity of kinetic observables is analyzed using a newly developed sum over histories representation of chemical kinetics. In the sum over histories representation, the concentrations of the chemical species are decomposed into the sum of probabilities for chemical pathways that follow molecules from reactants to products or intermediates. Unlike static flux methods for reaction path analysis, the sum over histories approach includes the explicit time dependence of the pathway probabilities. Using the sum over histories representation, the sensitivity of an observable with respect to a kinetic parameter such as a rate coefficient is then analyzed in terms of how that parameter affects the chemical pathway probabilities. The method is illustrated for species concentration target functions in H2 combustion where the rate coefficients are allowed to vary over their associated uncertainty ranges. It is found that large sensitivities are often associated with rate limiting steps along important chemical pathways or by reactions that control the branching of reactive flux. PMID:26493932

  3. Kinetics of Thermochemical Reactions Important in the Venus Atmospheric Sulfur Cycle

    NASA Technical Reports Server (NTRS)

    Fegley, Bruce, Jr.

    1997-01-01

    The purpose of this project was to experimentally measure the rates of several thermochemical gas-solid reactions between sulfur gases in the Venus atmosphere and reactive minerals on the hot Venus surface. Despite the great importance of these reactions for the maintenance of significant amounts of sulfur gases (and thus for the maintenance of the global cloud cover) in the atmosphere of Venus, essentially no kinetic data are currently available for them.

  4. The importance of sequential (x,n) reactions on element activation of fusion reactor materials

    NASA Astrophysics Data System (ADS)

    Cierjacks, S.; Hino, Y.

    1990-02-01

    The importance of sequential (x,n) reactions on element activation in fusion reactors is demonstrated by a few examples (Na, Mg, V, Cr) studied recently. It is shown that the time-dependent total element activity in some cases is strongly governed by contributions from such reactions at least for light and medium-weight elements and cooling times above more than 1 year.

  5. CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA

    EPA Science Inventory

    The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

  6. SUBSTITUTION REACTIONS FOR THE DETOXIFICATION OF HAZARDOUS CHEMICALS

    EPA Science Inventory

    Chemical Treatment is one of several treatment techniques used for the remediation of toxic and hazardous chemicals. Chemical treatment in this report is defined as substitution of halogens by hydrogens for the conversion of halogenated organic toxicant into its native hydrocarb...

  7. Mixing and chemical reaction in sheared and nonsheared homogeneous turbulence

    NASA Technical Reports Server (NTRS)

    Leonard, Andy D.; Hill, James C.

    1992-01-01

    Direct numerical simulations were made to examine the local structure of the reaction zone for a moderately fast reaction between unmixed species in decaying, homogeneous turbulence and in a homogeneous turbulent shear flow. Pseudospectral techniques were used in domains of 64 exp 3 and higher wavenumbers. A finite-rate, single step reaction between non-premixed reactants was considered, and in one case temperature-dependent Arrhenius kinetics was assumed. Locally intense reaction rates that tend to persist throughout the simulations occur in locations where the reactant concentration gradients are large and are amplified by the local rate of strain. The reaction zones are more organized in the case of a uniform mean shear than in isotropic turbulence, and regions of intense reaction rate appear to be associated with vortex structures such as horseshoe vortices and fingers seen in mixing layers. Concentration gradients tend to align with the direction of the most compressive principal strain rate, more so in the isotropic case.

  8. Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols

    ERIC Educational Resources Information Center

    Goodney, David E.

    2006-01-01

    Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the student's

  9. Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

    Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,

  10. Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols

    ERIC Educational Resources Information Center

    Goodney, David E.

    2006-01-01

    Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the student's…

  11. Mapping Students' Conceptual Modes When Thinking about Chemical Reactions Used to Make a Desired Product

    ERIC Educational Resources Information Center

    Weinrich, M. L.; Talanquer, V.

    2015-01-01

    The central goal of this qualitative research study was to uncover major implicit assumptions that students with different levels of training in the discipline apply when thinking and making decisions about chemical reactions used to make a desired product. In particular, we elicited different ways of conceptualizing why chemical reactions happen

  12. Method of operating a thermal engine powered by a chemical reaction

    DOEpatents

    Ross, John; Escher, Claus

    1988-01-01

    The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction.

  13. Method of operating a thermal engine powered by a chemical reaction

    DOEpatents

    Ross, J.; Escher, C.

    1988-06-07

    The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction. 7 figs.

  14. Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

    Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

  15. Introducing Stochastic Simulation of Chemical Reactions Using the Gillespie Algorithm and MATLAB: Revisited and Augmented

    ERIC Educational Resources Information Center

    Argoti, A.; Fan, L. T.; Cruz, J.; Chou, S. T.

    2008-01-01

    The stochastic simulation of chemical reactions, specifically, a simple reversible chemical reaction obeying the first-order, i.e., linear, rate law, has been presented by Martinez-Urreaga and his collaborators in this journal. The current contribution is intended to complement and augment their work in two aspects. First, the simple reversible

  16. Motivational Factors Contributing to Turkish High School Students' Achievement in Gases and Chemical Reactions

    ERIC Educational Resources Information Center

    Kadioglu, Cansel; Uzuntiryaki, Esen

    2008-01-01

    This study aimed to investigate the contribution of motivational factors to 10th grade students' achievement in gases and chemical reactions in chemistry. Three hundred fifty nine 10th grade students participated in the study. The Gases and Chemical Reactions Achievement Test and the Motivated Strategies for Learning Questionnaire were…

  17. Mapping Students' Conceptual Modes When Thinking about Chemical Reactions Used to Make a Desired Product

    ERIC Educational Resources Information Center

    Weinrich, M. L.; Talanquer, V.

    2015-01-01

    The central goal of this qualitative research study was to uncover major implicit assumptions that students with different levels of training in the discipline apply when thinking and making decisions about chemical reactions used to make a desired product. In particular, we elicited different ways of conceptualizing why chemical reactions happen…

  18. Design criteria for extraction with chemical reaction and liquid membrane permeation

    NASA Technical Reports Server (NTRS)

    Bart, H. J.; Bauer, A.; Lorbach, D.; Marr, R.

    1988-01-01

    The design criteria for heterogeneous chemical reactions in liquid/liquid systems formally correspond to those of classical physical extraction. More complex models are presented which describe the material exchange at the individual droplets in an extraction with chemical reaction and in liquid membrane permeation.

  19. Introducing Stochastic Simulation of Chemical Reactions Using the Gillespie Algorithm and MATLAB: Revisited and Augmented

    ERIC Educational Resources Information Center

    Argoti, A.; Fan, L. T.; Cruz, J.; Chou, S. T.

    2008-01-01

    The stochastic simulation of chemical reactions, specifically, a simple reversible chemical reaction obeying the first-order, i.e., linear, rate law, has been presented by Martinez-Urreaga and his collaborators in this journal. The current contribution is intended to complement and augment their work in two aspects. First, the simple reversible…

  20. Chemical kinetics in dynamic reaction fronts and in etching of self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Yen, Andrew Tze-Chung

    1997-11-01

    In recent years there has been great interest in studying systems where the reactants are initially separated in space. In this case, one can expect to find phenomenon exemplified by an interface or front that separates the reactants and persists in time. The presence of a reaction front is a characteristic of a variety of biological, chemical and physical processes. In this thesis we describe experimental and simulation results for several different reaction-diffusion systems with initially separated reactants. We describe an experimental study of a reversible A + B ↔ C reaction diffusion process with initially separated reactants in a convectionless capillary. We show that the dynamics of the system can be described in terms of a crossover between an 'irreversible' and a 'reversible' regime. Scaling exponents are derived. Rich spatio-temporal patterns were observed for competing reactions under initially separated conditions. The patterns are explained by a reaction-diffusion model. The reaction parameters that determine whether pattern formation is observable at the front are the difference in the microscopic reaction constants and in the concentrations of the competing species. Monte Carlo simulations for two different types of third- order reactions, A + A + A → 0 and A + 2B → 0, were performed for both one and two dimensional lattices. Our numerical results show that for the two-dimensional case the behavior of the reaction follows mean-field theory while in one dimension the result is 'anomalous'. Under initial separation of reactants the A + 2B → C reaction-diffusion experimental system exhibits the non- classical phenomena of reactant segregation and depletion-zone formation. The scaling exponents differ from the simple A + B → C system. A theoretical study of the early time behavior based on a perturbation analysis was derived and compares well with Monte Carlo simulation. The chemistry at the silica surface is a very important field, not only related to some traditional applications, such as chromatography and electrophoresis, but also to surface adhesion and microelectronic structures in silicon waffers. The etching process of organosilane self-assembled-monolayers was studied. The unusual power law dependence observed experimentally compares well with simulations based on a reaction-diffusion model.

  1. Phase and chemical equilibria in the transesterification reaction of vegetable oils with supercritical lower alcohols

    NASA Astrophysics Data System (ADS)

    Anikeev, V. I.; Stepanov, D. A.; Ermakova, A.

    2011-08-01

    Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters, participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification reaction of free fatty acids and the transesterification reaction of fatty acid triglycerides attained upon treatment with supercritical methanol are determined. Relying on our analysis of the obtained equilibria for the esterification reaction of fatty acids and the transesterification reaction of triglycerides attained upon treatment with lower alcohols, we select the optimum conditions for performing the reaction in practice.

  2. Chemical modeling of irreversible reactions in nuclear waste-water-rock systems

    SciTech Connect

    Wolery, T.J.

    1981-02-01

    Chemical models of aqueous geochemical systems are usually built on the concept of thermodynamic equilibrium. Though many elementary reactions in a geochemical system may be close to equilibrium, others may not be. Chemical models of aqueous fluids should take into account that many aqueous redox reactions are among the latter. The behavior of redox reactions may critically affect migration of certain radionuclides, especially the actinides. In addition, the progress of reaction in geochemical systems requires thermodynamic driving forces associated with elementary reactions not at equilibrium, which are termed irreversible reactions. Both static chemical models of fluids and dynamic models of reacting systems have been applied to a wide spectrum of problems in water-rock interactions. Potential applications in nuclear waste disposal range from problems in geochemical aspects of site evaluation to those of waste-water-rock interactions. However, much further work in the laboratory and the field will be required to develop and verify such applications of chemical modeling.

  3. Inducing all steps of a chemical reaction with the scanning tunneling microscope tip: towards single molecule engineering

    PubMed

    Hla; Bartels; Meyer; Rieder

    2000-09-25

    All elementary steps of a chemical reaction have been successfully induced on individual molecules with a scanning tunneling microscope (STM) in a controlled step-by-step manner utilizing a variety of manipulation techniques. The reaction steps involve the separation of iodine from iodobenzene by using tunneling electrons, bringing together two resultant phenyls mechanically by lateral manipulation and, finally, their chemical association to form a biphenyl molecule mediated by excitation with tunneling electrons. The procedures presented here constitute an important step towards the assembly of individual molecules out of simple building blocks in situ on the atomic scale. PMID:10991231

  4. New chemical reactions in methane at high temperatures and pressures

    SciTech Connect

    Culler, T.S.; Schiferl, D. )

    1993-01-21

    The authors have used a Merrill-Bassett diamond anvil cell and Raman spectroscopy to study methane at high pressures (up to 13 GPa) and high temperatures (up to 912 K). At 2.5-5.0 GPa and 912 K, methane photoreacts with the laser light used for Raman spectroscopy and forms a graphitelike soot compound. At room temperature and pressure the Raman spectrum of the new material has an intense peak with a frequency of 1597 cm[sup [minus]1]. At higher pressures and temperatures (10-13 GPa and 948 K) a sample of [sup 13]CD[sub 4] methane photoreacted with the laser light and formed a hard, clear, solid film. At 0.34 GPa and 300 K, this film had Raman peaks at 541 and 1605 cm[sup [minus]1]. The 541-cm[sup [minus]1] peak may correspond to the 550-cm[sup [minus]1] peak found in some diamondlike carbon (DLC) films formed by chemical vapor deposition (CVD), but the 1605-cm[sup [minus]1] peak does not appear to have any such counterpart. Other possible Raman peaks were masked by interference from the diamond anvils. Thus, while the hard, clear film has some similarities to CVD DLC films, some important differences and questions remain. 35 refs., 5 figs.

  5. Chemical Synthesis Accelerated by Paper Spray: The Haloform Reaction

    ERIC Educational Resources Information Center

    Bain, Ryan M.; Pulliam, Christopher J.; Raab, Shannon A.; Cooks, R. Graham

    2016-01-01

    In this laboratory, students perform a synthetic reaction in two ways: (i) by traditional bulk-phase reaction and (ii) in the course of reactive paper spray ionization. Mass spectrometry (MS) is used both as an analytical method and a means of accelerating organic syntheses. The main focus of this laboratory exercise is that the same ionization

  6. Chemical Synthesis Accelerated by Paper Spray: The Haloform Reaction

    ERIC Educational Resources Information Center

    Bain, Ryan M.; Pulliam, Christopher J.; Raab, Shannon A.; Cooks, R. Graham

    2016-01-01

    In this laboratory, students perform a synthetic reaction in two ways: (i) by traditional bulk-phase reaction and (ii) in the course of reactive paper spray ionization. Mass spectrometry (MS) is used both as an analytical method and a means of accelerating organic syntheses. The main focus of this laboratory exercise is that the same ionization…

  7. Numerical study of chemical reactions in a surface microdischarge tube with mist flow based on experiment

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Nishiyama, H.

    2014-03-01

    Recently, a water treatment method of spraying solution into a discharge region has been developed and shows high energy efficiency. In this study, a simulation model of a water treatment method using a surface microdischarge (SMD) tube with mist flow is proposed for further understanding the detailed chemical reactions. Our model has three phases (plasma, gas and liquid) and three simulation steps. The carrier gas is humid air including 2% or 3% water vapour. The chemical species diffusion characteristics in the SMD tube and the concentrations in a droplet are clarified in a wide pH interval. The simulation results show that the chemical species generated on the SMD tube inner wall are diffused to the central axis and dissolved into fine droplets. Especially, OH radicals dissolve into droplets a few mm away from the SMD tube wall because of acidification of the droplets. Furthermore, the hydrogen peroxide density, which is the most important indicator of a radical reaction in water, is influenced by the initial solution pH. This pH dependence results from ozone self-decomposition in water.

  8. Theoretical research program to study chemical reactions in AOTV bow shock tubes

    NASA Technical Reports Server (NTRS)

    Taylor, Peter R.

    1993-01-01

    The main focus was the development, implementation, and calibration of methods for performing molecular electronic structure calculations to high accuracy. These various methods were then applied to a number of chemical reactions and species of interest to NASA, notably in the area of combustion chemistry. Among the development work undertaken was a collaborative effort to develop a program to efficiently predict molecular structures and vibrational frequencies using energy derivatives. Another major development effort involved the design of new atomic basis sets for use in chemical studies: these sets were considerably more accurate than those previously in use. Much effort was also devoted to calibrating methods for computing accurate molecular wave functions, including the first reliable calibrations for realistic molecules using full CI results. A wide variety of application calculations were undertaken. One area of interest was the spectroscopy and thermochemistry of small molecules, including establishing small molecule binding energies to an accuracy rivaling, or even on occasion surpassing, the experiment. Such binding energies are essential input to modeling chemical reaction processes, such as combustion. Studies of large molecules and processes important in both hydrogen and hydrocarbon combustion chemistry were also carried out. Finally, some effort was devoted to the structure and spectroscopy of small metal clusters, with applications to materials science problems.

  9. Studies in photochemical smog chemistry. 1. Atmospheric chemistry of toulene. 2. Analysis of chemical reaction mechanisms for photochemical smog

    SciTech Connect

    Leone, J.A.

    1985-01-01

    This study focuses on two related topics in the gas phase organic chemistry of importance in urban air pollution. An experimental effort aimed at developing a new explicit reaction mechanism for the atmospheric photooxidation of toluene is described. This mechanism is tested using experimental data from both indoor and outdoor smog chamber facilities. The predictions of the new reaction mechanism are found to be in good agreement with both sets of experimental data. Additional simulations performed with the new mechanism are used to investigate various mechanistic paths. A theoretical analysis of lumped chemical reaction mechanisms for photochemical smog is presented. Included is a description of a new counter species analysis technique which can be used to analyze any complex chemical reaction mechanism. When applied to mechanisms for photochemical smog, this analysis is shown capable of providing answers to previously inaccessible questions such as the relative contributions of individual organics to photochemical ozone formation.

  10. The influence of the "cage effect" on the mechanism of reversible bimolecular multistage chemical reactions in solutions

    NASA Astrophysics Data System (ADS)

    Doktorov, Alexander B.

    2015-08-01

    Manifestations of the "cage effect" at the encounters of reactants are theoretically treated by the example of multistage reactions in liquid solutions including bimolecular exchange reactions as elementary stages. It is shown that consistent consideration of quasi-stationary kinetics of multistage reactions (possible only in the framework of the encounter theory) for reactions proceeding near reactants contact can be made on the basis of the concepts of a "cage complex." Though mathematically such a consideration is more complicated, it is more clear from the standpoint of chemical notions. It is established that the presence of the "cage effect" leads to some important effects not inherent in reactions in gases or those in solutions proceeding in the kinetic regime, such as the appearance of new transition channels of reactant transformation that cannot be caused by elementary event of chemical conversion for the given mechanism of reaction. This results in that, for example, rate constant values of multistage reaction defined by standard kinetic equations of formal chemical kinetics from experimentally measured kinetics can differ essentially from real values of these constants.

  11. Vicher: A Virtual Reality Based Educational Module for Chemical Reaction Engineering.

    ERIC Educational Resources Information Center

    Bell, John T.; Fogler, H. Scott

    1996-01-01

    A virtual reality application for undergraduate chemical kinetics and reactor design education, Vicher (Virtual Chemical Reaction Model) was originally designed to simulate a portion of a modern chemical plant. Vicher now consists of two programs: Vicher I that models catalyst deactivation and Vicher II that models nonisothermal effects in

  12. Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2009-08-01

    This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  13. Solvation and chemical reaction of sodium in water clusters

    NASA Astrophysics Data System (ADS)

    Bobbert, C.; Schulz, C. P.

    Nam(H2O)n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium atoms are picked up. At low sodium vapour pressure ( < 110-4 mbar) pure Na(H2O)n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 110-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster the reaction occurs in pairs as in the macroscopic reaction.

  14. Chemical reaction and equilibration mechanisms in detonation waves

    SciTech Connect

    Tarver, C. M., LLNL

    1997-07-01

    Experimental and theoretical evidence for the nonequilibrium Zeldovich-von Neumann-Doring (NEZND) theory of self-sustaining detonation is presented. High density, high temperature transition state theory is used to calculate unimolecular reaction rate constants for the initial decomposition of gaseous norbornene, liquid nitromethane, and solid, single crystal pentaerythritol tetranitrate as functions of shock temperature. The calculated rate constants are compared to those derived from experimental induction time measurements at various shock and detonation states. Uncertainties in the calculated shock and von Neumann spike temperatures are the main drawbacks to calculating these reaction rates. Nanosecond measurements of the shock temperatures of unreacted explosives are necessary to reduce these uncertainties.

  15. Product-state control of bi-alkali-metal chemical reactions

    SciTech Connect

    Meyer, Edmund R.; Bohn, John L.

    2010-10-15

    We consider ultracold, chemically reactive scattering collisions of the diatomic molecules KRb. When two such molecules collide in an ultracold gas, we find that they are energetically forbidden from reacting to form the trimer species K{sub 2}Rb or Rb{sub 2}K, and hence can only react via the bond-swapping reaction 2KRb{yields}K{sub 2}+Rb{sub 2}. Moreover, the tiny energy released in this reaction can in principle be set to zero by applying electric or microwave fields, implying a means of controlling the available reaction channels in a chemical reaction.

  16. Classification of chemical substances, reactions, and interactions: The effect of expertise

    NASA Astrophysics Data System (ADS)

    Stains, Marilyne Nicole Olivia

    2007-12-01

    This project explored the strategies that undergraduate and graduate chemistry students engaged in when solving classification tasks involving microscopic (particulate) representations of chemical substances and microscopic and symbolic representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention while classifying, identifying the patterns of reasoning that they follow, and comparing the performance of students with different levels of preparation in the discipline. In general, our results suggest that advanced levels of expertise in chemical classification do not necessarily evolve in a linear and continuous way with academic training. Novice students had a tendency to reduce the cognitive demand of the task and rely on common-sense reasoning; they had difficulties differentiating concepts (conceptual undifferentiation) and based their classification decisions on only one variable (reduction). These ways of thinking lead them to consider extraneous features, pay more attention to explicit or surface features than implicit features and to overlook important and relevant features. However, unfamiliar levels of representations (microscopic level) seemed to trigger deeper and more meaningful thinking processes. On the other hand, expert students classified entities using a specific set of rules that they applied throughout the classification tasks. They considered a larger variety of implicit features and the unfamiliarity with the microscopic level of representation did not affect their reasoning processes. Consequently, novices created numerous small groups, few of them being chemically meaningful, while experts created few but large chemically meaningful groups. Novices also had difficulties correctly classifying entities in chemically meaningful groups. Finally, expert chemists in our study used classification schemes that are not necessarily traditionally taught in classroom chemistry (e.g. the structure of substances is more relevant to them than their composition when classifying substances as compounds or elements). This result suggests that practice in the field may develop different types of knowledge framework than those usually presented in chemistry textbooks.

  17. Theoretical Studies of Chemical Reactions following Electronic Excitation

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.

    2003-01-01

    The use of multi-configurational wave functions is demonstrated for several processes: tautomerization reactions in the ground and excited states of the DNA base adenine, dissociation of glycine molecule after electronic excitation, and decomposition/deformation of novel rare gas molecules HRgF. These processes involve bond brealung/formation and require multi-configurational approaches that include dynamic correlation.

  18. Chemical Principles Revisited. Redox Reactions and the Electropotential Axis.

    ERIC Educational Resources Information Center

    Vella, Alfred J.

    1990-01-01

    This paper suggests a nontraditional pedagogic approach to the subject of redox reactions and electrode potentials suitable for freshman chemistry. Presented is a method for the representation of galvanic cells without the introduction of the symbology and notation of conventional cell diagrams. (CW)

  19. Theoretical studies of the dynamics of chemical reactions

    SciTech Connect

    Wagner, A.F.

    1993-12-01

    Recent research effort has focussed on several reactions pertinent to combustion. The formation of the formyl radical from atomic hydrogen and carbon monoxide, recombination of alkyl radicals and halo-alkyl radicals with halogen atoms, and the thermal dissociation of hydrogen cyanide and acetylene have been studied by modeling. In addition, the inelastic collisions of NCO with helium have been investigated.

  20. Role of Conformational Structures and Torsional Anharmonicity in Controlling Chemical Reaction Rates and Relative Yields: Butanal + HO2 Reactions

    SciTech Connect

    Zheng, Jingjing; Seal, Prasenjit; Truhlar, Donald G.

    2013-01-01

    Aldehyderadical reactions are important in atmospheric and combustion chemistry, and the reactions studied here also serve more generally to illustrate a fundamental aspect of chemical kinetics that has been relatively unexplored from a quantitative point of view, in particular the roles of multiple structures and torsional anharmonicity in determining the rate constants and branching ratios (product yields). We consider hydrogen abstraction from four carbon sites of butanal (carbonyl-C, a-C, b-C and g-C) by hydroperoxyl radical. We employed multi-structural variational transition state theory for studying the first three channels; this uses a multi-faceted dividing surface and allows us to include the contributions of multiple structures of both reacting species and transition states. Multiconfigurational Shepard interpolation (MCSI) was used to obtain the geometries and energies of the potential energy surface along the minimum-energy paths, with gradients and Hessians calculated by the M08-HX/maug-cc-pVTZ method. We find the numbers of structures obtained for the transition states are 46, 60, 72 and 76respectively for the H abstraction at the carbonyl C, the a position, the b position and the g position. Our results show that neglecting the factors arising from multiple structures and torsional anharmonicity would lead to errors at 300, 1000 and 2400 K of factors of 8, 11 and 10 for abstraction at the carbonyl-O, 2, 11 and 25 at the a-C position, 2, 23 and 47 at the b-C position, and 0.6, 8 and 18 at the g-C position. The errors would be even larger at high temperature for the reverse of the H abstraction at the b-C. Relative yields are changed as much as a factor of 7.0 at 200 K, a factor of 5.0 at 298 K, and a factor of 3.7 in the other direction at 2400 K. The strong dependence of the product ratios on the multi-structural anharmonicity factors shows that such factors play an important role in controlling branching ratios in reaction mechanism networks.

  1. Characterization of Chemically Modified Enzymes for Bioremediation Reactions

    SciTech Connect

    Davison, Brian H.

    2000-12-31

    Remediation processes frequently involve species possessing limited solubility in water. For this project, we were interested in novel strategies using molecularly modified enzymes with enhanced activity and stability for remediation of recalcitrant compounds in organic solvents. Performance of naturally occurring enzymes is usually quite limited in such organic environments. The primary objective of the work was to gain a fundamental understanding of the molecular and catalytic properties of enzymes that have been chemically modified so that they are catalytically active and chemically stable in organic solvents. The premise was that stabilized and activated enzymes, which can function under harsh chemical conditions, are optimally suited for bioremediation in nonaqueous media where substrates of interest are more soluble and processed with greater efficiency. This unique strategy was examined with respect to the degradation of chlorophenols and PCBs.

  2. Tattoo-Associated Skin Reaction: The Importance of an Early Diagnosis and Proper Treatment

    PubMed Central

    Bassi, Andrea; Campolmi, Piero; Cannarozzo, Giovanni; Conti, Rossana; Bruscino, Nicola; Gola, Massimo; Ermini, Stefano; Massi, Daniela; Moretti, Silvia

    2014-01-01

    Tattoo is going to be a very common practice especially among young people and we are witnessing a gradual increase of numerous potential complications to tattoo placement which are often seen by physicians, but generally unknown to the public. The most common skin reactions to tattoo include a transient acute inflammatory reaction due to trauma of the skin with needles and medical complications such as superficial and deep local infections, systemic infections, allergic contact dermatitis, photodermatitis, granulomatous and lichenoid reactions, and skin diseases localized on tattooed area (eczema, psoriasis, lichen, and morphea). Next to these inflammatory skin reactions we have to consider also the possibility of the development of cutaneous conditions such as pseudolymphomatous reactions and pseudoepitheliomatous hyperplasia. The aim of this study is to underline the importance of an early diagnosis by performing a histological examination especially when we are in front of suspected papulonodular lesions arising from a tattoo, followed by a proper treatment, since cutaneous neoplastic evolution is known to be a rare but possible complication. PMID:25147796

  3. NEURAL - a tracking detector for neutron-induced reactions of astrophysical importance

    NASA Astrophysics Data System (ADS)

    Martin, L.; Buchmann, L.; Carpino, J. F.; Chen, A.; Couture, A.; Davids, B.; Fallis, J.; Fox, S. P.; Hager, U.; Hussein, A.; Laird, A. M.; Olchanski, K.; Ottewell, D.; Ruiz, C.; Ruprecht, G.; Sheffer, G.; Sjue, S.; Tengblad, O.; Tovesson, F.

    2011-09-01

    Observations from gamma ray telescopes indicate that most of the galactic 26Al originates in massive stars. Several sites have been discussed for its production, including proton burning in the winds of very massive stars, and the later, explosive burning stages of these stars. Observations from the RHESSI and INTEGRAL missions currently seem to point to the latter scenario. In the advanced burning stages of massive stars the presence of neutrons becomes an important factor in nuclear reaction networks, so in addition to the 26Al(p,γ)27Si reaction the neutron capture reactions 26Al(n,p)26Mg and 26Al(n,α)23Na can lead to the destruction of 26Al, and thus alter the observed 26Al abundance. NEURAL is a detector design to measure the excitation functions of these reactions over a wide range of energies. 26Al targets implanted at TRIUMF will be exposed to a pulsed neutron beam at the neutron time-of-flight facility at LANSCE (Los Alamos Neutron Science CEnter). NEURAL is designed to detect all charged reaction products, combining a time projection chamber for the heavy ions, and Si detectors for the light particles mounted around the target. A first prototype has been built and partially tested at TRIUMF and LANSCE in December 2009.

  4. Control of a chemical reaction (photodegradation of the p3ht polymer) with nonlocal dielectric environments

    NASA Astrophysics Data System (ADS)

    Peters, V. N.; Tumkur, T. U.; Zhu, G.; Noginov, M. A.

    2015-10-01

    Proximity to metallic surfaces, plasmonic structures, cavities and other inhomogeneous dielectric environments is known to control spontaneous emission, energy transfer, scattering, and many other phenomena of practical importance. The aim of the present study was to demonstrate that, in spirit of the Marcus theory, the rates of chemical reactions can, too, be influenced by nonlocal dielectric environments, such as metallic films and metal/dielectric bilayer or multilayer structures. We have experimentally shown that metallic, composite metal/dielectric substrates can, indeed, control ordering as well as photodegradation of thin poly-3-hexylthiophene (p3ht) films. In many particular experiments, p3ht films were separated from metal by a dielectric spacer, excluding conventional catalysis facilitated by metals and making modification of the nonlocal dielectric environment a plausible explanation for the observed phenomena. This first step toward understanding of a complex relationship between chemical reactions and nonlocal dielectric environments is to be followed by the theory development and a broader scope of thorough experimental studies.

  5. Control of a chemical reaction (photodegradation of the p3ht polymer) with nonlocal dielectric environments

    PubMed Central

    Peters, V. N.; Tumkur, T. U.; Zhu, G.; Noginov, M. A.

    2015-01-01

    Proximity to metallic surfaces, plasmonic structures, cavities and other inhomogeneous dielectric environments is known to control spontaneous emission, energy transfer, scattering, and many other phenomena of practical importance. The aim of the present study was to demonstrate that, in spirit of the Marcus theory, the rates of chemical reactions can, too, be influenced by nonlocal dielectric environments, such as metallic films and metal/dielectric bilayer or multilayer structures. We have experimentally shown that metallic, composite metal/dielectric substrates can, indeed, control ordering as well as photodegradation of thin poly-3-hexylthiophene (p3ht) films. In many particular experiments, p3ht films were separated from metal by a dielectric spacer, excluding conventional catalysis facilitated by metals and making modification of the nonlocal dielectric environment a plausible explanation for the observed phenomena. This first step toward understanding of a complex relationship between chemical reactions and nonlocal dielectric environments is to be followed by the theory development and a broader scope of thorough experimental studies. PMID:26434679

  6. Identifying Nuclear Reaction Rates That Are Important For (44) TI Supernova Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    The, L.-S.; Meyer, B. S.; Clayton, D. D.

    1997-05-01

    Large excesses of (44) Ca in certain presolar graphite and silicon carbide grains give strong evidence for (44) Ti production in supernovae. Furthermore, recent detection of the (44) Ti gamma -line from the Cas A SNR by CGRO/COMPTEL shows that radioactive (44) Ti is produced in supernovae. In this work we study the conditions needed for (44) Ti production in alpha-rich freezeouts in core-collapse supernovae as a function of peak temperature and density. We survey the key nuclear reactions governing (44) Ti production by varying their cross sections. We identify and rank their importance. We find (44) Ti production is most sensitive to variations in the rates of the reactions (44) Ti(alpha ,p)(47) V, alpha (2alpha ,gamma )(12) C, and (45) V(p,gamma )(46) Cr. Because many of these rates are unknown experimentally, our results suggest the most important targets for future cross section measurements.

  7. EFFICIENT CHEMICAL TRANSFORMATIONS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA

    EPA Science Inventory

    The diverse nature of chemical entities requires various green' strategic pathways in our quest towards attaining sustainability. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable...

  8. X-ray Microspectroscopy and Chemical Reactions in Soil Microsites

    SciTech Connect

    D Hesterberg; M Duff; J Dixon; M Vepraskas

    2011-12-31

    Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

  9. Chemical reaction and equilibration mechanisms in detonation waves

    SciTech Connect

    Tarver, C.M.

    1998-07-01

    Experimental and theoretical evidence for the nonequilibrium Zeldovich-von Neumann-Doring (NEZND) theory of self-sustaining detonation is presented. High density, high temperature transition state theory is used to calculate unimolecular reaction rate constants for the initial decomposition of gaseous norbornene, liquid nitromethane, and solid, single crystal pentaerythritol tetranitrate as functions of shock temperature. The calculated rate constants are compared to those derived from experimental induction time measurements at various shock and detonation states. Uncertainties in the calculated shock and von Neumann spike temperatures are the main drawbacks to calculating these reaction rates. Nanosecond measurements of the shock temperatures of unreacted explosives are necessary to reduce these uncertainties. {copyright} {ital 1998 American Institute of Physics.}

  10. Magnetohydrodynamic (MHD) stretched flow of nanofluid with power-law velocity and chemical reaction

    NASA Astrophysics Data System (ADS)

    Hayat, Tasawar; Rashid, Madiha; Imtiaz, Maria; Alsaedi, Ahmed

    2015-11-01

    This paper deals with the boundary layer flow of nanofluid over power-law stretched surface. Analysis has been carried out in the presence of applied magnetic field and chemical reaction. Heat and mass transfer characteristics are studied using heat and mass convective conditions. The governing partial differential equations are transferred to the nonlinear ordinary differential equations. Convergent series solutions are obtained for fluid velocity, temperature and concentrations fields. Influences of pertinent parameters including Hartman number, thermal and concentration Biot numbers and chemical reaction parameters are discussed on the velocity, temperature and concentration profiles. Graphical result are presented and discussed. Computations for local Nusselt and Sherwood numbers are carried out. It is observed that the heat transfer rate is enhanced by increasing power-law index, thermal Biot number and chemical reaction parameter while mass transfer rate increases for power-law index and chemical reaction parameter.

  11. EVALUATION OF CHEMICAL REACTION MECHANISMS FOR PHOTOCHEMICAL SMOG. PART 2. QUANTITATIVE EVALUATION OF THE MECHANISMS (REVISED)

    EPA Science Inventory

    Six chemical reaction mechanisms for photochemical smog were analyzed to determine why, under identical conditions, they predict different maximum ozone concentrations. To perform the analysis, a counter species technique was used to determine the contributions of individual reac...

  12. LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, Krishnan; Bittker, David A.

    1993-01-01

    A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

  13. Concept Maps as a Tool for Teaching Organic Chemical Reactions.

    PubMed

    ket, Barbara; Aleksij Glaar, Saa; Vogrinc, Janez

    2015-01-01

    The purpose of the research was to establish the impact of the application of a concept map in chemistry lessons on the effective solving of tasks with organic reactions content. In the first phase of the research, a concept map was produced representing the reactions of hydrocarbons, organic halogenated compounds and organic oxygen compounds, and in the second phase the produced concept map was introduced in lessons. Its impact was tested on a sample consisting of 186 students (average age of 17.8 years), who were divided into a control group (88 students) and an experimental group (98 students). Prior to the experiment, the two groups were equalised in terms of their level of development of formal logical thinking and their average grade in chemistry. A knowledge test, consisting of five problem tasks comprising multiple parts, was used as a quantitative instrument for measuring the impact of the applied concept map. The content of the knowledge test was selected on the basis of the chemistry lesson plan (reactions of organic oxygen compounds) for general upper secondary schools (in Slovenian: gimnazije). An analysis of the task solving showed statistically significant differences in the responses of the experimental group members and the control group members (experimental group M = 15.9; SD = 6.33; control group M = 13.6; SD = 7.93; p = 0.03). The produced concept map contributed to the more effective interrelation of concepts and, consequently, to more effective problem task solving. PMID:26085431

  14. Theoretical approach to modelling the low-barrier chemical reactions initiated by pulsed electron beam

    NASA Astrophysics Data System (ADS)

    Aktaev, N. E.

    2014-11-01

    A possibility to analyze low-barrier chemical reactions induced by electron beam is proposed within the framework of generalization of classical Kramers approach. A relationship for calculation of chemical reaction rate is received for potential barriers comparable with energy of system. It has been shown that results of our approach agree with results of dynamical modeling within 2% not only in the area of applicability of classical (Kramers) approach but also more widely.

  15. Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes

    PubMed Central

    Kabbani, Mohamad A.; Tiwary, Chandra Sekhar; Autreto, Pedro A.S.; Brunetto, Gustavo; Som, Anirban; Krishnadas, K.R.; Ozden, Sehmus; Hackenberg, Ken P.; Gong, Yongi; Galvao, Douglas S.; Vajtai, Robert; Kabbani, Ahmad T.; Pradeep, Thalappil; Ajayan, Pulickel M.

    2015-01-01

    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations. PMID:26073564

  16. Indoor Volatile Organic Compounds and Chemical Sensitivity Reactions

    PubMed Central

    Win-Shwe, Tin-Tin; Arashidani, Keiichi; Kunugita, Naoki

    2013-01-01

    Studies of unexplained symptoms observed in chemically sensitive subjects have increased the awareness of the relationship between neurological and immunological diseases due to exposure to volatile organic compounds (VOCs). However, there is no direct evidence that links exposure to low doses of VOCs and neurological and immunological dysfunction. We review animal model data to clarify the role of VOCs in neuroimmune interactions and discuss our recent studies that show a relationship between chronic exposure of C3H mice to low levels of formaldehyde and the induction of neural and immune dysfunction. We also consider the possible mechanisms by which VOC exposure can induce the symptoms presenting in patients with a multiple chemical sensitivity. PMID:24228055

  17. Large-scale prediction of adverse drug reactions using chemical, biological, and phenotypic properties of drugs

    PubMed Central

    Liu, Mei; Wu, Yonghui; Chen, Yukun; Sun, Jingchun; Zhao, Zhongming; Chen, Xue-wen; Matheny, Michael Edwin

    2012-01-01

    Objective Adverse drug reaction (ADR) is one of the major causes of failure in drug development. Severe ADRs that go undetected until the post-marketing phase of a drug often lead to patient morbidity. Accurate prediction of potential ADRs is required in the entire life cycle of a drug, including early stages of drug design, different phases of clinical trials, and post-marketing surveillance. Methods Many studies have utilized either chemical structures or molecular pathways of the drugs to predict ADRs. Here, the authors propose a machine-learning-based approach for ADR prediction by integrating the phenotypic characteristics of a drug, including indications and other known ADRs, with the drug's chemical structures and biological properties, including protein targets and pathway information. A large-scale study was conducted to predict 1385 known ADRs of 832 approved drugs, and five machine-learning algorithms for this task were compared. Results This evaluation, based on a fivefold cross-validation, showed that the support vector machine algorithm outperformed the others. Of the three types of information, phenotypic data were the most informative for ADR prediction. When biological and phenotypic features were added to the baseline chemical information, the ADR prediction model achieved significant improvements in area under the curve (from 0.9054 to 0.9524), precision (from 43.37% to 66.17%), and recall (from 49.25% to 63.06%). Most importantly, the proposed model successfully predicted the ADRs associated with withdrawal of rofecoxib and cerivastatin. Conclusion The results suggest that phenotypic information on drugs is valuable for ADR prediction. Moreover, they demonstrate that different models that combine chemical, biological, or phenotypic information can be built from approved drugs, and they have the potential to detect clinically important ADRs in both preclinical and post-marketing phases. PMID:22718037

  18. Non-stationary filtration mode during chemical reactions with the gas phase

    NASA Astrophysics Data System (ADS)

    Zavialov, Ivan; Konyukhov, Andrey; Negodyaev, Sergey

    2015-04-01

    An experimental and numerical study of filtration accompanied by chemical reactions between displacing fluid and solid skeleton is considered. Glass balls (400-500 μm in diameter) were placed in 1 cm gap between two glass sheets and were used as model porous medium. The baking soda was added to the glass balls. The 70% solution of acetic acid was used as the displacer. The modeling porous medium was saturated with a mineral oil, and then 70% solution of colored acetic acid was pumped through the medium. The glass balls and a mineral oil have a similar refractive index, so the model porous medium was optically transparent. During the filtration, the gas phase was generated by the chemical reactions between the baking soda and acetic acid, and time-dependent displacement of the chemical reaction front was observed. The front of the chemical reaction was associated with the most intensive gas separation. The front moved, stopped, and then moved again to the area where it had been already. We called this process a secondary oxidation wave. To describe this effect, we added to the balance equations a term associated with the formation and disappearance of phases due to chemical reactions. The equations were supplemented by Darcy's law for multiphase filtration. Nonstationarity front propagation of the chemical reaction in the numerical experiment was observed at Damköhler numbers greater than 100. The mathematical modelling was agreed well with the experimental results.

  19. Light-induced nitrous acid (HONO) production from NO2 heterogeneous reactions on household chemicals

    NASA Astrophysics Data System (ADS)

    Gómez Alvarez, Elena; Sörgel, Matthias; Gligorovski, Sasho; Bassil, Sabina; Bartolomei, Vincent; Coulomb, Bruno; Zetzsch, Cornelius; Wortham, Henri

    2014-10-01

    Nitrous acid (HONO) can be generated in various indoor environments directly during combustion processes or indirectly via heterogeneous NO2 reactions with water adsorbed layers on diverse surfaces. Indoors not only the concentrations of NO2 are higher but the surface to volume (S/V) ratios are larger and therefore the potential of HONO production is significantly elevated compared to outdoors. It has been claimed that the UV solar light is largely attenuated indoors. Here, we show that solar light (λ > 340 nm) penetrates indoors and can influence the heterogeneous reactions of gas-phase NO2 with various household surfaces. The NO2 to HONO conversion mediated by light on surfaces covered with domestic chemicals has been determined at atmospherically relevant conditions i.e. 50 ppb NO2 and 50% RH. The formation rates of HONO were enhanced in presence of light for all the studied surfaces and are determined in the following order: 1.3·109 molecules cm-2 s-1 for borosilicate glass, 1.7·109 molecules cm-2 s-1 for bathroom cleaner, 1.0·1010 molecules cm-2 s-1 on alkaline detergent (floor cleaner), 1.3·1010 molecules cm-2 s-1 for white wall paint and 2.7·1010 molecules cm-2 s-1 for lacquer. These results highlight the potential of household chemicals, used for cleaning purposes to generate HONO indoors through light-enhanced NO2 heterogeneous reactions. The results obtained have been applied to predict the timely evolution of HONO in a real indoor environment using a dynamic mass balance model. A steady state mixing ratio of HONO has been estimated at 1.6 ppb assuming a contribution from glass, paint and lacquer and considering the photolysis of HONO as the most important loss process.

  20. Application of genetic algorithms to a detailed chemical reaction system for secondary organic aerosol formation

    NASA Astrophysics Data System (ADS)

    Xia, A.; Stroud, C.; Makar, P.

    2009-12-01

    An explicit chemical mechanism is instrumental to modeling secondary organic aerosol (SOA) formation. It is, however, difficult to implement an explicit mechanism in a 3-dimensional air quality model because of the high computational cost caused by a large number of reactions and organic species involved. To address this issue, a new simplified chemical reaction system is first proposed for ?-pinene SOA formation, which uses the volatility-basis set speciation for condensable products. The simple reaction system reflects the evolution of chemical species from a near-explicit master chemical mechanism (MCM) and it also unifies reactions between SOA precursors with different oxidants under different conditions. A total of 440 unknown parameters (product yields of parameterized products, reaction rates, etc.) from the new reaction system are estimated by using multi-objective genetic algorithms operating on the detailed mechanism. The number of species was reduced from 300 in the detailed mechanism to 30 in the simplified mechanism. Output species profiles, obtained from original subset of MCM reactions for ?-pinene oxidation, are reproduced for scenarios under a wide range of HC/NOx conditions. Ultimately, the same unified simple reaction system with updated parameters could be used to describe the SOA formation from different precursors.

  1. Consistency and Inconsistency in A Level Students' Understandings of a Number of Chemical Reactions.

    ERIC Educational Resources Information Center

    Kwen, Boo Hong

    1996-01-01

    Explores A level students' conceptions of some common chemical reactions. Findings indicate that students apply frameworks consistently across groups of events that they perceive to be similar. What was found to be lacking was the scientists' view of all the reactions being regarded as realizations of the same underlying conceptual model. Contains…

  2. RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    NASA Astrophysics Data System (ADS)

    Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

    2013-03-01

    We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines.

  3. Ca + HF - The anatomy of a chemical insertion reaction

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.; Pattengill, M. D.; Mascarello, F. G.; Zare, R. N.

    1987-01-01

    A comprehensive first-principles theoretical investigation of the gas phase reaction Ca + HF - CaF + H is reported. Ab initio potential energy calculations are first discussed, along with characteristics of the computed potential energy surface. Next, the fitting of the computed potential energy points to a suitable analytical functional form is described, and maps of the fitted potential surface are displayed. The methodology and results of a classical trajectory calculation utilizing the fitted potential surface are presented. Finally, the significance of the trajectory study results is discussed, and generalizations concerning dynamical aspects of Ca + HF scattering are drawn.

  4. The Modification of Biocellular Chemical Reactions by Environmental Physicochemicals

    NASA Astrophysics Data System (ADS)

    Ishido, M.

    Environmental risk factors affect human biological system to different extent from modification of biochemical reaction to cellular catastrophe. There are considerable public concerns about electromagnetic fields and endocrine disruptors. Their risk assessments have not been fully achieved because of their scientific uncertainty: electromagnetic fields just modify the bioreaction in the restricted cells and endocrine disruptors are quite unique in that their expression is dependent on the exposure periods throughout a life. Thus, we here describe their molecular characterization to establish the new risk assessments for environmental physicochemicals.

  5. Quantum chemical study of penicillin: Reactions after acylation

    NASA Astrophysics Data System (ADS)

    Li, Rui; Feng, Dacheng; Zhu, Feng

    The density functional theory methods were used on the model molecules of penicillin to determine the possible reactions after their acylation on ?-lactamase, and the results were compared with sulbactam we have studied. The results show that, the acylated-enzyme tetrahedral intermediate can evolves with opening of ?-lactam ring as well as the thiazole ring; the thiazole ring-open products may be formed via ?-lactam ring-open product or from tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. In virtue of the water-assisted, their energy barriers are obviously reduced.

  6. Real World of Industrial Chemistry: Ethylene: The Organic Chemical Industry's Most Important Building Block.

    ERIC Educational Resources Information Center

    Fernelius, W. Conrad, Ed.; And Others

    1979-01-01

    The value of ethylene, as the organic chemical industry's most important building block, is discussed. The discussion focuses on the source of ethylene, its various forms and functions, and the ways in which the forms are made. (SA)

  7. Development of a novel fingerprint for chemical reactions and its application to large-scale reaction classification and similarity.

    PubMed

    Schneider, Nadine; Lowe, Daniel M; Sayle, Roger A; Landrum, Gregory A

    2015-01-26

    Fingerprint methods applied to molecules have proven to be useful for similarity determination and as inputs to machine-learning models. Here, we present the development of a new fingerprint for chemical reactions and validate its usefulness in building machine-learning models and in similarity assessment. Our final fingerprint is constructed as the difference of the atom-pair fingerprints of products and reactants and includes agents via calculated physicochemical properties. We validated the fingerprints on a large data set of reactions text-mined from granted United States patents from the last 40 years that have been classified using a substructure-based expert system. We applied machine learning to build a 50-class predictive model for reaction-type classification that correctly predicts 97% of the reactions in an external test set. Impressive accuracies were also observed when applying the classifier to reactions from an in-house electronic laboratory notebook. The performance of the novel fingerprint for assessing reaction similarity was evaluated by a cluster analysis that recovered 48 out of 50 of the reaction classes with a median F-score of 0.63 for the clusters. The data sets used for training and primary validation as well as all python scripts required to reproduce the analysis are provided in the Supporting Information. PMID:25541888

  8. Analytical Solution of Steady State Equations for Chemical Reaction Networks with Bilinear Rate Laws

    PubMed Central

    Halsz, dm M.; Lai, Hong-Jian; McCabe, Meghan M.; Radhakrishnan, Krishnan; Edwards, Jeremy S.

    2014-01-01

    True steady states are a rare occurrence in living organisms, yet their knowledge is essential for quasi-steady state approximations, multistability analysis, and other important tools in the investigation of chemical reaction networks (CRN) used to describe molecular processes on the cellular level. Here we present an approach that can provide closed form steady-state solutions to complex systems, resulting from CRN with binary reactions and mass-action rate laws. We map the nonlinear algebraic problem of finding steady states onto a linear problem in a higher dimensional space. We show that the linearized version of the steady state equations obeys the linear conservation laws of the original CRN. We identify two classes of problems for which complete, minimally parameterized solutions may be obtained using only the machinery of linear systems and a judicious choice of the variables used as free parameters. We exemplify our method, providing explicit formulae, on CRN describing signal initiation of two important types of RTK receptor-ligand systems, VEGF and EGF-ErbB1. PMID:24334389

  9. Kinetics of thermochemical gas-solid reactions important in the Venus sulfur cycle

    NASA Technical Reports Server (NTRS)

    Fegley, Bruce, Jr.

    1988-01-01

    The thermochemical net reaction CaCO3 + SO2 yields CaSO4 + CO is predicted to be an important sink for incorporation of SO2 into the Venus crust. The reaction rate law was established to understand the dependence of rate on experimental variables such as temperature and partial pressure of SO2, CO2, and O2. The experimental approach was a variant of the thermogravimetric method often employed to study the kinetics of thermochemical gas-solid reactions. Clear calcite crystals were heated at constant temperature in SO2-bearing gas streams for varying time periods. Reaction rate was determined by three independent methods. A weighted linear least squares fit to all rate data yielded a rate equation. Based on the Venera 13, 14 and Vega 2 observations of CaO content of the Venus atmosphere, SO2 at the calculated rate would be removed from the Venus atmosphere in about 1,900,00 years. The most plausible endogenic source of the sulfur needed to replenish atmospheric SO2 is volcanism. The annual amount of erupted material needed for the replenishment depends on sulfur content; three ratios are used to calculate rates ranging from 0.4 to 11 cu km/year. This geochemically derived volcanism rate can be used to test if geophysically derived rates are correct. The work also suggests that Venus is less volcanically active than the Earth.

  10. Polarization of molecular angular momentum in the chemical reactions Li + HF and F + HD

    NASA Astrophysics Data System (ADS)

    Krasilnikov, Mikhail B.; Popov, Ruslan S.; Roncero, Octavio; De Fazio, Dario; Cavalli, Simonetta; Aquilanti, Vincenzo; Vasyutinskii, Oleg S.

    2013-06-01

    The quantum mechanical approach to vector correlation of angular momentum orientation and alignment in chemical reactions [G. Balint-Kurti and O. S. Vasyutinskii, J. Phys. Chem. A 113, 14281 (2009)], 10.1021/jp902796v is applied to the molecular reagents and products of the Li + HF [L. Gonzalez-Sanchez, O. S. Vasyutinskii, A. Zanchet, C. Sanz-Sanz, and O. Roncero, Phys. Chem. Chem. Phys. 13, 13656 (2011)], 10.1039/c0cp02452j and F + HD [D. De Fazio, J. Lucas, V. Aquilanti, and S. Cavalli, Phys. Chem. Chem. Phys. 13, 8571 (2011)], 10.1039/c0cp02738c reactions for which accurate scattering information has become recently available through time-dependent and time-independent approaches. Application of the theory to two important particular cases of the reactive collisions has been considered: (i) the influence of the angular momentum polarization of reactants in the entrance channel on the spatial distribution of the products in the exit channel and (ii) angular momentum polarization of the products of the reaction between unpolarized reactants. In the former case, the role of the angular momentum alignment of the reactants is shown to be large, particularly when the angular momentum is perpendicular to the reaction scattering plane. In the latter case, the orientation and alignment of the product angular momentum was found to be significant and strongly dependent on the scattering angle. The calculation also reveals significant differences between the vector correlation properties of the two reactions under study which are due to difference in the reaction mechanisms. In the case of F + HD reaction, the branching ratio between HF and DF production points out interest in the insight gained into the detailed dynamics, when information is available either from exact quantum mechanical calculations or from especially designed experiments. Also, the geometrical arrangement for the experimental determination of the product angular momentum orientation and alignment based on a compact and convenient spherical tensor expression for the intensity of the resonance enhanced multiphoton ionization (REMPI 2 + 1) signal is suggested.

  11. Theoretical Chemical Dynamics Studies of Elementary Combustion Reactions

    SciTech Connect

    Donald L. Thompson

    2009-09-30

    The objective of this research was to develop and apply methods for more accurate predictions of reaction rates based on high-level quantum chemistry. We have developed and applied efficient, robust methods for fitting global ab initio potential energy surfaces (PESs) for both spectroscopy and dynamics calculations and for performing direct dynamics simulations. Our approach addresses the problem that high-level quantum calculations are often too costly in computer time for practical applications resulting in the use of levels of theory that are often inadequate for reactions. A critical objective was to develop practical methods that require the minimum number of electronic structure calculations for acceptable fidelity to the ab initio PES. Our method does this by a procedure that determines the optimal configurations at which ab initio points are computed, and that ensures that the final fitted PES is uniformly accurate to a prescribed tolerance. Our fitting methods can be done automatically, with little or no human intervention, and with no prior knowledge of the topology of the PES. The methods are based on local fitting schemes using interpolating moving least-squares (IMLS). IMLS has advantages over the very effective modified-Shepard methods developed by Collins and others in that higher-order polynomials can be used and does not require derivatives but can benefit from them if available.

  12. Evolution of Autocatalytic Sets in Computational Models of Chemical Reaction Networks.

    PubMed

    Hordijk, Wim

    2016-06-01

    Several computational models of chemical reaction networks have been presented in the literature in the past, showing the appearance and (potential) evolution of autocatalytic sets. However, the notion of autocatalytic sets has been defined differently in different modeling contexts, each one having some shortcoming or limitation. Here, we review four such models and definitions, and then formally describe and analyze them in the context of a mathematical framework for studying autocatalytic sets known as RAF theory. The main results are that: (1) RAF theory can capture the various previous definitions of autocatalytic sets and is therefore more complete and general, (2) the formal framework can be used to efficiently detect and analyze autocatalytic sets in all of these different computational models, (3) autocatalytic (RAF) sets are indeed likely to appear and evolve in such models, and (4) this could have important implications for a possible metabolism-first scenario for the origin of life. PMID:26499126

  13. Synthesis and chemical reactions of the steroidal hormone 17α-methyltestosterone.

    PubMed

    El-Desoky, El-Sayed Ibrahim; Reyad, Mahmoud; Afsah, Elsayed Mohammed; Dawidar, Abdel-Aziz Mahmoud

    2016-01-01

    Structural modifications of natural products with complex structures like steroids require great synthetic effort. A review of literature is presented on the chemistry of the steroidal hormone 17α-methyltestosterone that is approved by Food and Drug Administration (FDA) in the United States as an androgen for estrogen-androgen hormone replacement therapy treatment. The analog also offers special possibilities for the prevention/treatment of hormone-sensitive cancers. The testosterone skeleton has important functionalities in the molecule that can act as a carbonyl component, an active methylene compound, α,β-unsaturated enone and tertiary hydroxyl group in various chemical reactions to access stereoisomeric steroidal compounds with potent activity. In addition, microbiological methods of synthesis and transformation of this hormone are presented. PMID:26639430

  14. Evolution of Autocatalytic Sets in Computational Models of Chemical Reaction Networks

    NASA Astrophysics Data System (ADS)

    Hordijk, Wim

    2015-10-01

    Several computational models of chemical reaction networks have been presented in the literature in the past, showing the appearance and (potential) evolution of autocatalytic sets. However, the notion of autocatalytic sets has been defined differently in different modeling contexts, each one having some shortcoming or limitation. Here, we review four such models and definitions, and then formally describe and analyze them in the context of a mathematical framework for studying autocatalytic sets known as RAF theory. The main results are that: (1) RAF theory can capture the various previous definitions of autocatalytic sets and is therefore more complete and general, (2) the formal framework can be used to efficiently detect and analyze autocatalytic sets in all of these different computational models, (3) autocatalytic (RAF) sets are indeed likely to appear and evolve in such models, and (4) this could have important implications for a possible metabolism-first scenario for the origin of life.

  15. Students' Ideas about How and Why Chemical Reactions Happen: Mapping the Conceptual Landscape

    ERIC Educational Resources Information Center

    Yan, Fan; Talanquer, Vicente

    2015-01-01

    Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative

  16. WORKSHOP ON STATUS OF TEST METHODS FOR ASSESSING POTENTIAL OF CHEMICALS TO INDUCE RESPIRATORY ALLERGIC REACTIONS

    EPA Science Inventory

    Because of the association between allergy and asthma and the increasing incidence of morbidity and mortality due to asthma, there is growing concern over the potential of industrial chemicals to produce allergic reactions in the respiratory tract. Two classes of chemicals have b...

  17. Students' Ideas about How and Why Chemical Reactions Happen: Mapping the Conceptual Landscape

    ERIC Educational Resources Information Center

    Yan, Fan; Talanquer, Vicente

    2015-01-01

    Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative…

  18. KEMOD: A mixed chemical kinetic and equilibrium model of aqueous and solid phase geochemical reactions

    SciTech Connect

    Yeh, G.T.; Iskra, G.A.; Szecsody, J.E.; Zachara, J.M.; Streile, G.P.

    1995-01-01

    This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.

  19. The mineralogic evolution of the Martian surface through time: Implications from chemical reaction path modeling studies

    NASA Technical Reports Server (NTRS)

    Plumlee, G. S.; Ridley, W. I.; Debraal, J. D.; Reed, M. H.

    1993-01-01

    Chemical reaction path calculations were used to model the minerals that might have formed at or near the Martian surface as a result of volcano or meteorite impact driven hydrothermal systems; weathering at the Martian surface during an early warm, wet climate; and near-zero or sub-zero C brine-regolith reactions in the current cold climate. Although the chemical reaction path calculations carried out do not define the exact mineralogical evolution of the Martian surface over time, they do place valuable geochemical constraints on the types of minerals that formed from an aqueous phase under various surficial and geochemically complex conditions.

  20. Rate constants for chemical reactions in high-temperature nonequilibrium air

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1986-01-01

    In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

  1. Shock-Induced Chemical Reactions of Polycyclic Aromatic Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Elert, Mark; Zybin, Sergey; Revell, Shannon; White, Carter

    2006-03-01

    Polycyclic aromatic hydrocarbons (PAHs) have been found in the atmospheres of Jupiter and Titan, and also in meteorites, interplanetary dust, and circumstellar graphite grains. The ubiquity of these complex organic structures and their stability under extreme conditions make them a significant factor in discussions of brebiotic chemistry in the solar system. To study the shock-induced chemistry of PAHs under conditions appropriate for astrophysical impacts, molecular dynamics simulations have been carried out for solid naphthalene and anthracene using a reactive empirical potential. The major reaction channels for these two closely related compounds were found to be substantially different. Product distributions were also found to depend strongly on the orientation of the PAH crystal relative to the shock propagation direction.

  2. High temperature chemical kinetic study of the H2-CO-CO2-NO reaction system

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.

    1975-01-01

    An experimental study of the kinetics of the H2-CO-CO2-NO reaction system was made behind incident shock waves at temperatures of 2460 and 2950 K. The overall rate of the reaction was measured by monitoring radiation from the CO + O yields CO2 + h upoilon reaction. Correlation of these data with a detailed reaction mechanism showed that the high-temperature rate of the reaction N + OH yields NO + H can be described by the low-temperature (320 K) rate coefficient. Catalytic dissociation of molecular hydrogen was an important reaction under the tests conditions.

  3. Electron-vibration entanglement in the Born-Oppenheimer description of chemical reactions and spectroscopy.

    PubMed

    McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S; Reimers, Jeffrey R

    2015-10-14

    Entanglement is sometimes regarded as the quintessential measure of the quantum nature of a system and its significance for the understanding of coupled electronic and vibrational motions in molecules has been conjectured. Previously, we considered the entanglement developed in a spatially localized diabatic basis representation of the electronic states, considering design rules for qubits in a low-temperature chemical quantum computer. We extend this to consider the entanglement developed during high-energy processes. We also consider the entanglement developed using adiabatic electronic basis, providing a novel way for interpreting effects of the breakdown of the Born-Oppenheimer (BO) approximation. We consider: (i) BO entanglement in the ground-state wavefunction relevant to equilibrium thermodynamics, (ii) BO entanglement associated with low-energy wavefunctions relevant to infrared and tunneling spectroscopies, (iii) BO entanglement in high-energy eigenfunctions relevant to chemical reaction processes, and (iv) BO entanglement developed during reactive wavepacket dynamics. A two-state single-mode diabatic model descriptive of a wide range of chemical phenomena is used for this purpose. The entanglement developed by BO breakdown correlates simply with the diameter of the cusp introduced by the BO approximation, and a hierarchy appears between the various BO-breakdown correction terms, with the first-derivative correction being more important than the second-derivative correction which is more important than the diagonal correction. This simplicity is in contrast to the complexity of BO-breakdown effects on thermodynamic, spectroscopic, and kinetic properties. Further, processes poorly treated at the BO level that appear adequately treated using the Born-Huang adiabatic approximation are found to have properties that can only be described using a non-adiabatic description. For the entanglement developed between diabatic electronic states and the nuclear motion, qualitatively differently behavior is found compared to traditional properties of the density matrix and hence entanglement provides new information about system properties. For chemical reactions, this type of entanglement simply builds up as the transition-state region is crossed. It is robust to small changes in parameter values and is therefore more attractive for making quantum qubits than is the related fragile ground-state entanglement, provided that coherent motion at the transition state can be sustained. PMID:26204101

  4. Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Minitti, M. P.; Budarz, J. M.; Kirrander, A.; Robinson, J. S.; Ratner, D.; Lane, T. J.; Zhu, D.; Glownia, J. M.; Kozina, M.; Lemke, H. T.; Sikorski, M.; Feng, Y.; Nelson, S.; Saita, K.; Stankus, B.; Northey, T.; Hastings, J. B.; Weber, P. M.

    2015-06-01

    Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

  5. Influence of mineral weathering reactions on the chemical composition of soil water, springs, and ground water, Catoctin Mountains, Maryland

    USGS Publications Warehouse

    Katz, B.G.

    1989-01-01

    During 1983 and 1984, wet precipitation was primarily a solution of dilute sulphuric acid, whereas calcium and bicarbonate were the major ions in springs and ground water in two small watersheds with a deciduous forest cover in central Maryland. Dominant ions in soil water were calcium, magnesium, and sulphate. The relative importance of mineral weathering reactions on the chemical composition of these subsurface waters was compared to the contribution from wet precipitation, biological processes, and road deicing salts. -from Author

  6. Electric field suppression of ultracold confined chemical reactions

    SciTech Connect

    Quemener, Goulven; Bohn, John L.

    2010-06-15

    We consider ultracold collisions of polar molecules confined in a one-dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking {sup 40}K{sup 87}Rb molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes for KRb molecules to be 1 s. We find a ratio of elastic to quenching collision rates of about 100, which may be sufficient to achieve efficient evaporative cooling of polar KRb molecules.

  7. Students' Dilemmas in Reaction Stoichiometry Problem Solving: Deducing the Limiting Reagent in Chemical Reactions

    ERIC Educational Resources Information Center

    Chandrasegaran, A. L.; Treagust, David F.; Waldrip, Bruce G.; Chandrasegaran, Antonia

    2009-01-01

    A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four reaction stoichiometry problems. Students' written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations…

  8. Students' Dilemmas in Reaction Stoichiometry Problem Solving: Deducing the Limiting Reagent in Chemical Reactions

    ERIC Educational Resources Information Center

    Chandrasegaran, A. L.; Treagust, David F.; Waldrip, Bruce G.; Chandrasegaran, Antonia

    2009-01-01

    A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four reaction stoichiometry problems. Students' written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations

  9. Thermochemical model for shock-induced chemical reactions in porous thermite: The heat detonation model

    SciTech Connect

    Boslough, M.B.

    1989-01-01

    A thermochemical model has been developed that treats a shock-induced solid state chemical reaction as a special type of detonation, called a ''heat detonation'' to distinguish it from an ordinary explosive detonation and describe the final form that the chemical energy takes. According to shock temperature measurements, chemical energy can be released from porous reactive solids on a time scale shorter than shock-transit times in laboratory samples. By comparing the experimental shock temperature for porous thermite to that calculated by the model, the amount of thermite reacted when shocked to about 4 GPa was estimated to be between 60 and 70%. Calculated shock temperatures are extremely strong functions of the extent of reaction, but are relatively insensitive to the initial porosity and amount of volatile impurities. Thus, shock temperature measurements are the most useful for real-time studies of shock-induced exothermic chemical reactions in solids. 11 refs., 5 figs., 1 tab.

  10. Nonequilibrium chemical potentials and free energies for enzyme-catalyzed reactions.

    PubMed

    Keizer, J

    1987-12-01

    Using the statistical theory of nonequilibrium thermodynamics we explore the nature of nonequilibrium corrections to chemical potentials in simple enzyme-catalyzed reactions. The statistical definition of the chemical potential, which pertains to systems that are at stable steady states, is applied to the Michaelis-Menten reaction scheme in a cellular-sized compartment that communicates with outside reservoirs. Calculations based on the kinetic parameters for hexokinase and triose phosphate isomerase show that substantial corrections to the chemical potential of product (the order of 25 mV) are possible if the reaction is sufficiently far from equilibrium. The dependence of the corrections to the chemical potentials on the size of the cellular compartment are explored, and the relevance of the corrections for understanding the thermodynamics of metabolites is discussed. PMID:2450667

  11. Momentum balance equation for nonelectrolytes in models of coupling between chemical reaction and diffusion in membranes.

    PubMed

    Ga?dzicki, Z; Miekisz, S

    1984-04-01

    The role of viscosity in coupling between chemical reaction (complex formation) and diffusion in membranes has been investigated. The Fick law was replaced by the momentum balance equation with the viscous term. The irreversible thermodynamics admits coupling of the chemical reaction rate with the gradient of velocity. The proposed model has shown the contrary effect of viscosity and confirmed the experimental results. The chemical reaction rate increases only above the limit value of viscosity. The parameter Q (degree of complex formation) was introduced to investigate coupling. Q equals to the ratio of the chemical contribution into the flux of the complex to the total flux of the substance transported. For different values of the parameters of the model the dependence of Q upon position inside the membrane has been numerically calculated. The assumptions of the model limit it to a specific case and they only roughly model the biological situation. PMID:6537360

  12. Effect of water treatment chemicals on limestone/sulfur dioxide reaction in flue gas desulfurization systems

    SciTech Connect

    Dille, E.R.; Gaikwad, R.P.

    1994-12-31

    A simple laboratory test has been developed which simulates the reaction between limestone/water and sulfur dioxide in flue gas desulfurization systems. By adding various chemicals, in differing concentrations, to the limestone/water mixture, the quantitative impact on the sulfur dioxide/limestone reaction can be qualified and quantified. This paper will present the impact of several water treatment chemicals on the reaction of limestone and sulfur dioxide. An attempt has been made to predict the effect through mathematical correlations. All of the additive chemicals tend to decrease the rate of dissolution of limestone to various degrees. Some of the chemicals retard crystal growth thus adversely impacting solids separation in the thickener. The physical appearance of the crystal growth retarded limestone absorber slurry approaches a colloidal suspension.

  13. A New Method for Describing the Mechanism of a Chemical Reaction Based on the Unified Reaction Valley Approach.

    PubMed

    Zou, Wenli; Sexton, Thomas; Kraka, Elfi; Freindorf, Marek; Cremer, Dieter

    2016-02-01

    The unified reaction valley approach (URVA) used for a detailed mechanistic analysis of chemical reactions is improved in three different ways: (i) Direction and curvature of path are analyzed in terms of internal coordinate components that no longer depend on local vibrational modes. In this way, the path analysis is no longer sensitive to path instabilities associated with the occurrences of imaginary frequencies. (ii) The use of third order terms of the energy for a local description of the reaction valley allows an extension of the URVA analysis into the pre- and postchemical regions of the reaction path, which are typically characterized by flat energy regions. (iii) Configurational and conformational processes of the reaction complex are made transparent even in cases where these imply energy changes far less than a kcal/mol by exploiting the topology of the potential energy surface. As examples, the rhodium-catalyzed methanol carbonization, the Diels-Alder reaction between 1,3-butadiene and ethene, and the rearrangement of HCN to CNH are discussed. PMID:26734810

  14. Theoretical study of thermodynamic properties and reaction rates of importance in the high-speed research program

    NASA Technical Reports Server (NTRS)

    Langhoff, Stephen; Bauschlicher, Charles; Jaffe, Richard

    1992-01-01

    One of the primary goals of NASA's high-speed research program is to determine the feasibility of designing an environmentally safe commercial supersonic transport airplane. The largest environmental concern is focused on the amount of ozone destroying nitrogen oxides (NO(x)) that would be injected into the lower stratosphere during the cruise portion of the flight. The limitations placed on NO(x) emission require more than an order of magnitude reduction over current engine designs. To develop strategies to meet this goal requires first gaining a fundamental understanding of the combustion chemistry. To accurately model the combustor requires a computational fluid dynamics approach that includes both turbulence and chemistry. Since many of the important chemical processes in this regime involve highly reactive radicals, an experimental determination of the required thermodynamic data and rate constants is often very difficult. Unlike experimental approaches, theoretical methods are as applicable to highly reactive species as stable ones. Also our approximation of treating the dynamics classically becomes more accurate with increasing temperature. In this article we review recent progress in generating thermodynamic properties and rate constants that are required to understand NO(x) formation in the combustion process. We also describe our one-dimensional modeling efforts to validate an NH3 combustion reaction mechanism. We have been working in collaboration with researchers at LeRC, to ensure that our theoretical work is focused on the most important thermodynamic quantities and rate constants required in the chemical data base.

  15. Complex chemical zoning in eclogite facies garnet reaction rims: the role of grain boundary diffusion

    NASA Astrophysics Data System (ADS)

    Prenzel, J.; Abart, R.; Keller, L.

    2009-03-01

    In metapelites of the Saualpe complex (Eastern Alps) continuous 10 m to 20 m wide garnet reaction rims formed along biotite-plagioclase and biotite-perthite interfaces. The pre-existing mineral assemblages are remnants of low pressure high temperature metamorphism of Permian age. The garnet reaction rims grew during the Cretaceous eclogite facies overprint. Reaction rim growth involved transfer of Fe and Mg components from the garnet-biotite interface to the garnet-feldspar interface and transfer of the Ca component in the opposite direction. The garnets show complex, asymmetrical chemical zoning, which reflects the relative contributions of short circuit diffusion along grain boundaries within the polycrystalline garnet reaction rims and volume diffusion through the grain interiors on bulk mass transfer. It is demonstrated by numerical modelling that the spacing of the grain boundaries, i.e. the grain size of the garnet in the reaction rim is a first order control on its internal chemical zoning.

  16. Experimental results of exothermic reaction with concentration gradient catalyst in a solar chemical heat pump

    SciTech Connect

    Takashima, Takumi; Doi, Takuya; Ando, Yuji; Tanaka, Tadayoshi; Miyahara, Ryosuke; Kamoshida, Junji

    1997-12-31

    Solar chemical heat pump can upgrade the low temperature solar heat about 80 C to about 150--200 C by the reversible chemical reactions of 2-propanol/acetone/hydrogen, which are composed of endothermic and exothermic reactions. In the exothermic process of above reaction, a temperature peak occurs near the inlet of reaction zone in the case of arranging catalyst uniformly. Such a temperature distribution is not suitable for heat exchange. Therefore, the authors arrange the concentration of catalyst gradationally so as not to occur the temperature peak. In this paper, experimental results of exothermic reaction with concentration gradient catalyst in a double tubular exothermic reactor are presented. These results show that the arrangement of concentration gradient catalyst has the possibility about the temperature control in the catalytic reactor.

  17. Mixing and chemical reaction in an idealized swirl chamber

    SciTech Connect

    Knio, O.M.; Worlikar, A.S.; Najm, H.N.

    1996-01-01

    A vorticity-based, low-Mach-number model for simulating combustion in closed chambers is constructed. Numerical scheme is based on a mixed finite-difference pseudo-spectral discretization of the governing equations. Discrete evolution equations are integrated in time using a predictor-corrector scheme, while discrete elliptic systems are inverted with the help of fast-Poisson solver. Scheme is applied to analyze mixing and combustion in an idealized swirl cavity, which consists of the annular space between a spinning inner cylinder and a stationary reaction. To this end, we assume that the oxidizer and fuel are initially separated by a thin mixed region, and carefully control mixing levels by varying the duration of the swirl-driven mixing period. The mixture is then ignited along the boundary of the inner cylinder. When pre-mixing is complete, an axisymmetric flame front is established, and the reactants are consumed as the front propagates radially outwards. When the charge is partially mixed, combustion in the early stages predominantly occurs within a non-uniform premixed front. As this non-uniform front approaches the outer cylinder, a transition to a distributed combustion regime occurs. Following the transition, the remaining fuel burns at a slow rate within non-premixed flames which wrap around the inner cylinder. Results show that the mixing time has substantial effects on the pressure rise within the cavity and on the evolution of the burnt fraction, and that these effects become more pronounced as the Damkoehler number increases.

  18. Chemical reactions in a scramjet combustor and two-dimensional nozzles

    NASA Astrophysics Data System (ADS)

    Yeung, Moon-Tai

    Finite-rate chemistry of hydrogen-air combustion is to be investigated numerically in a one-dimensional constant pressure SCRAMJET combustor and two-dimensional nozzles. Detailed reaction mechanisms and temperature dependent thermodynamics are to be used in the models. The aspects of interest include the combustion characteristics at different fuel-air ratios, pressures and initial temperatures in the combustor. Methods for enhancing the combustion rate in the combustor is to be studied also. The effect of expansion rate on the hydrogen-air reactions is the prime focus of the nozzle calculation. The results from different inlet conditions and wall geometries are to be analyzed. A computer model for a one-dimensional (channel-flow) combustor is constructed based on the chemical kinetics subroutine library CHEMKIN. Subsequent calculations show that the initial temperature is the most important parameter in the combustor. It is further discovered that certain reaction steps are responsible for the initial delay exhibited in all hydrogen-air combustion processes. Low temperature behavior is studied extensively and augmentation methods are developed. The introduction of a small percentage of the hydrogen radical into the initial mixture is found to be the most effective in reducing the reaction delay. The combustor pressure enters the overall reaction process in a linear manner. The calculations over five combustor pressures show that the initial delay in hydrogen-air reaction and the following period of explosion are proportional to the combustor pressure raised to certain powers. The nozzle model is two-dimensional, steady and inviscid with no conductivity and diffusivity. Two schemes are developed to handle the boundary conditions. One is based on pure numerical interpolation/extrapolation methods while the other imposes analytical supersonic characteristic equations. The former scheme is found to be more efficient while the latter is more accurate. In analysing the response of the combustion product to an expansion, it is found that the formation of water is favoured by an expansion. A closer examination reveals that the behavior can be attributed to the abundance of free radicals in the nozzle inlet composition. Freezing is not clearly observed except for the NO_x species.

  19. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    DOE R&D Accomplishments Database

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  20. Weber's Law for Biological Responses in Autocatalytic Networks of Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Inoue, Masayo; Kaneko, Kunihiko

    2011-07-01

    Biological responses often obey Weber’s law, according to which the magnitude of the response depends only on the fold change in the external input. In this study, we demonstrate that a system involving a simple autocatalytic reaction shows such a response when a chemical is slowly synthesized by the reaction from a faster influx process. We also show that an autocatalytic reaction process occurring in series or in parallel can obey Weber’s law with an oscillatory adaptive response. Considering the simplicity and ubiquity of the autocatalytic process, our proposed mechanism is thought to be commonly observed in biological reactions.

  1. Weber's law for biological responses in autocatalytic networks of chemical reactions.

    PubMed

    Inoue, Masayo; Kaneko, Kunihiko

    2011-07-22

    Biological responses often obey Weber's law, according to which the magnitude of the response depends only on the fold change in the external input. In this study, we demonstrate that a system involving a simple autocatalytic reaction shows such a response when a chemical is slowly synthesized by the reaction from a faster influx process. We also show that an autocatalytic reaction process occurring in series or in parallel can obey Weber's law with an oscillatory adaptive response. Considering the simplicity and ubiquity of the autocatalytic process, our proposed mechanism is thought to be commonly observed in biological reactions. PMID:21867048

  2. 78 FR 52801 - Importer of Controlled Substances; Notice of Application; Chattem Chemicals, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-26

    ... to import narcotic raw material are not appropriate. 72 FR 3417(2007). Any bulk manufacturer who is... (f). As noted in a previous notice published in the Federal Register on September 23, 1975, 40 FR... Enforcement Administration Importer of Controlled Substances; Notice of Application; Chattem Chemicals,...

  3. 78 FR 69131 - Importer of Controlled Substances, Notice of Registration, Chattem Chemicals, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-18

    ... Enforcement Administration Importer of Controlled Substances, Notice of Registration, Chattem Chemicals, Inc. By Notice dated August 15, 2013, and published in the Federal Register on August 26, 2013, 78 FR... requests for hearings on applications to import narcotic raw material are not appropriate. 72 FR 3417...

  4. 78 FR 5498 - Importer of Controlled Substances; Notice of Registration; Chattem Chemicals, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-25

    ... Enforcement Administration Importer of Controlled Substances; Notice of Registration; Chattem Chemicals, Inc. By Notice dated June 28, 2012, and published in the Federal Register on July 6, 2012, 77 FR 40086... for hearing on applications to import narcotic raw material are not appropriate, 72 FR...

  5. 77 FR 43861 - Importer of Controlled Substances; Notice of Application; Boehringer Ingelheim Chemicals

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-26

    ... Enforcement Administration Importer of Controlled Substances; Notice of Application; Boehringer Ingelheim..., Boehringer Ingelheim Chemicals, Inc., 2820 N. Normandy Drive, Petersburg, Virginia 23805, made application by..., 40 FR 43745-46, all applicants for registration to import a basic class of any controlled...

  6. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule

    NASA Astrophysics Data System (ADS)

    Zheng, Peng; Arantes, Guilherme M.; Field, Martin J.; Li, Hongbin

    2015-06-01

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions.

  7. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule

    PubMed Central

    Zheng, Peng; Arantes, Guilherme M.; Field, Martin J.; Li, Hongbin

    2015-01-01

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions. PMID:26108369

  8. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule.

    PubMed

    Zheng, Peng; Arantes, Guilherme M; Field, Martin J; Li, Hongbin

    2015-01-01

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions. PMID:26108369

  9. Programming chemical kinetics: engineering dynamic reaction networks with DNA strand displacement

    NASA Astrophysics Data System (ADS)

    Srinivas, Niranjan

    Over the last century, the silicon revolution has enabled us to build faster, smaller and more sophisticated computers. Today, these computers control phones, cars, satellites, assembly lines, and other electromechanical devices. Just as electrical wiring controls electromechanical devices, living organisms employ "chemical wiring" to make decisions about their environment and control physical processes. Currently, the big difference between these two substrates is that while we have the abstractions, design principles, verification and fabrication techniques in place for programming with silicon, we have no comparable understanding or expertise for programming chemistry. In this thesis we take a small step towards the goal of learning how to systematically engineer prescribed non-equilibrium dynamical behaviors in chemical systems. We use the formalism of chemical reaction networks (CRNs), combined with mass-action kinetics, as our programming language for specifying dynamical behaviors. Leveraging the tools of nucleic acid nanotechnology (introduced in Chapter 1), we employ synthetic DNA molecules as our molecular architecture and toehold-mediated DNA strand displacement as our reaction primitive. Abstraction, modular design and systematic fabrication can work only with well-understood and quantitatively characterized tools. Therefore, we embark on a detailed study of the "device physics" of DNA strand displacement (Chapter 2). We present a unified view of strand displacement biophysics and kinetics by studying the process at multiple levels of detail, using an intuitive model of a random walk on a 1-dimensional energy landscape, a secondary structure kinetics model with single base-pair steps, and a coarse-grained molecular model that incorporates three-dimensional geometric and steric effects. Further, we experimentally investigate the thermodynamics of three-way branch migration. Our findings are consistent with previously measured or inferred rates for hybridization, fraying, and branch migration, and provide a biophysical explanation of strand displacement kinetics. Our work paves the way for accurate modeling of strand displacement cascades, which would facilitate the simulation and construction of more complex molecular systems. In Chapters 3 and 4, we identify and overcome the crucial experimental challenges involved in using our general DNA-based technology for engineering dynamical behaviors in the test tube. In this process, we identify important design rules that inform our choice of molecular motifs and our algorithms for designing and verifying DNA sequences for our molecular implementation. We also develop flexible molecular strategies for "tuning" our reaction rates and stoichiometries in order to compensate for unavoidable non-idealities in the molecular implementation, such as imperfectly synthesized molecules and spurious "leak" pathways that compete with desired pathways. We successfully implement three distinct autocatalytic reactions, which we then combine into a de novo chemical oscillator. Unlike biological networks, which use sophisticated evolved molecules (like proteins) to realize such behavior, our test tube realization is the first to demonstrate that Watson-Crick base pairing interactions alone suffice for oscillatory dynamics. Since our design pipeline is general and applicable to any CRN, our experimental demonstration of a de novo chemical oscillator could enable the systematic construction of CRNs with other dynamic behaviors.

  10. Effect of gravity field on the nonequilibrium/nonlinear chemical oscillation reactions

    NASA Astrophysics Data System (ADS)

    Fujieda, S.; Mori, Y.; Nakazawa, A.; Mogami, Y.

    2001-01-01

    Biological systems have evolved for a long time under the normal gravity. The Belousov-Zhabotinsky (BZ) reaction is a nonlinear chemical system far from the equilibrium that may be considered as a simplified chemical model of the biological systems so as to study the effect of gravity. The reaction solution is comprised of bromate in sulfuric acid as an oxidizing agent, 1,4-cyclohexanedione as an organic substrate, and ferroin as a metal catalyst. Chemical waves in the BZ reaction-diffusion system are visualized as blue and red patterns of ferriin and ferroin, respectively. After an improvement to the tubular reaction vessels in the experimental setup, the traveling velocity of chemical waves in aqueous solutions was measured in time series under normal gravity, microgravity, hyper-gravity, and normal gravity using the free-fall facility of JAMIC (Japan Microgravity Center), Hokkaido, Japan. Chemical patterns were collected as image data via CCD camera and analyzed by the software of NIH image after digitization. The estimated traveling velocity increased with increasing gravity as expected. It was clear experimentally that the traveling velocity of target patterns in reaction diffusion system was influenced by the effect of convection and correlated closely with the gravity field.

  11. Analysis of turbulent free-jet hydrogen-air diffusion flames with finite chemical reaction rates

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.; Glass, I. I.; Evans, J. S.

    1979-01-01

    A numerical analysis is presented of the nonequilibrium flow field resulting from the turbulent mixing and combustion of an axisymmetric hydrogen jet in a supersonic parallel ambient air stream. The effective turbulent transport properties are determined by means of a two-equation model of turbulence. The finite-rate chemistry model considers eight elementary reactions among six chemical species: H, O, H2O, OH, O2 and H2. The governing set of nonlinear partial differential equations was solved by using an implicit finite-difference procedure. Radial distributions were obtained at two downstream locations for some important variables affecting the flow development, such as the turbulent kinetic energy and its dissipation rate. The results show that these variables attain their peak values on the axis of symmetry. The computed distribution of velocity, temperature, and mass fractions of the chemical species gives a complete description of the flow field. The numerical predictions were compared with two sets of experimental data. Good qualitative agreement was obtained.

  12. Numerical Modeling of Coupled Variably-Saturated Fluid Flow and Reactive Transport with Fast and Slow Chemical Reactions

    SciTech Connect

    LI, MING-HSU; SIEGEL, MALCOLM D.; YEH, GOUR-TSYH

    1999-09-20

    The couplings among chemical reaction rates, advective and diffusive transport in fractured media or soils, and changes in hydraulic properties due to precipitation and dissolution within fractures and in rock matrix are important for both nuclear waste disposal and remediation of contaminated sites. This paper describes the development and application of LEHGC2.0, a mechanistically-based numerical model for simulation of coupled fluid flow and reactive chemical transport including both fast and slow reactions invariably saturated media. Theoretical bases and numerical implementations are summarized, and two example problems are demonstrated. The first example deals with the effect of precipitation-dissolution on fluid flow and matrix diffusion in a two-dimensional fractured media. Because of the precipitation and decreased diffusion of solute from the fracture into the matrix, retardation in the fractured medium is not as large as the case wherein interactions between chemical reactions and transport are not considered. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions.

  13. Measurement of Helical Trajectories in Chemical Reactions by Ion Imaging

    SciTech Connect

    Cline, Joseph I.

    2003-02-10

    During the first year of this grant we developed methods to measure the sense of rotation of the nitric oxide molecule (NO) using a circularly polarized laser probe and with ion imaging detection. The method was applied to the measurement of the correlation of rotational angular momentum orientation with recoil direction in the photodissociation of NO{sub 2}. [''Detection of ''ended'' NO recoil in the 355 nm NO2 photodissociation mechanism'', V.K. Nestorov and J.I. Cline, J. Chem. Phys. 111, 5287-5290 (1999)]. The photodissociation work was performed at the University of Nevada with additional, partial support from NSF. In the summer of 1999 this technique was transported to and implemented at the Combustion Research Facility at Sandia National Laboratory in Livermore, CA in a study of rotationally inelastic collisions of NO molecules with Ar atoms. The summer 1999 experiments at Sandia demonstrated that it is possible to detect collision-induced rotational alignment (preferred planes of rotation) for product molecules. During the late summer and fall of 1999 the P.I. and student James Barr developed a theoretical method for quantifying the angular momentum alignment and for extracting it from ion images. During the winter and spring of 2000 (January-May) the P.I. was in residence at Sandia National Laboratory in Livermore during a sabbatical leave from the University of Nevada. During this time the P.I. collaborated with Sandia P.I. Dr. David Chandler and Sandia postdoctorals Thomas Lorenz and Elisabeth Wade in experiments measuring both rotational alignment and rotational orientation (preferred senses of rotation) in collisions of NO with Ar. Graduate student James Barr continued these experiments at Sandia through the end of June 2000. The success of our experimental techniques for measuring collisional alignment and the theoretical methods we have developed for extracting quantitative alignment parameters from ion images. Spectroscopic probing of products by resonance-enhanced multiphoton ionization (REMPI) detected by ion imaging is a powerful method for measuring the product state-resolved differential cross section (DCS) of bimolecular scattering reactions. Polarization of the REMPI probe light also makes imaging data potentially sensitive to product angular momentum polarization, as is well known from imaging studies of photodissociation. We exploit this sensitivity to obtain the state-resolved product angular momentum polarization as a function of recoil angle. Previous measurements of molecular angular momentum polarization in bimolecular scattering have either been constrained to detection in the scattering plane or have averaged around the azimuthal angle of the recoil velocity vector in the collision frame. Imaging detection captures the entire product recoil velocity sphere, enabling a more complete determination of product angular momentum polarization than is possible for experiments of lower detection dimensionality.

  14. Chemically Activated Formation of Organic Acids in Reactions of the Criegee Intermediate with Aldehydes and Ketones

    SciTech Connect

    Jalan, Amrit; Allen, Joshua W.; Green, William H.

    2013-08-08

    Reactions of the Criegee intermediate (CI, .CH2OO.) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between .CH2OO. and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48–51 kcal mol-1 lower in energy, formed via 1,3- cycloaddition of .CH2OO. across the CQO bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O–O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO o CH3CHO o CH3COCH3 (the highest yield being 10-4 times lower than the initial .CH2OO. concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.

  15. Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

    NASA Astrophysics Data System (ADS)

    Chia, A.; Tan, K. C.; Pawela, Ł.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.

    2016-03-01

    Classical chemical kinetics uses rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, in other words, a reaction that contains only incoherent transitions. A prominent example of a reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator that determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts the same recombination dephasing rate as the conventional Haberkorn model, which is consistent with recent experiments [K. Maeda et al., J. Chem. Phys. 139, 234309 (2013), 10.1063/1.4844355], in contrast to previous work by Jones and Hore [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010), 10.1016/j.cplett.2010.01.063]. The standard radical-pair reaction has conventionally been described by either a normalized density operator incorporating both the radical pair and reaction products or a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalized and refers only to radical-pair states. Generalizations to include additional dephasing processes and an arbitrary number of sites are also discussed.

  16. Is there a motivation for a universal behaviour in molecular populations undergoing chemical reactions?

    PubMed

    Stanislavsky, A; Weron, K

    2013-10-01

    Many chemical reactions demonstrate a very similar evolution of reagent concentrations in time, although their species are quite different. This can be linked with a universal stochastic behavior of reagents. In this paper we show what role in understanding chemical kinetics stochastic models play. To support this concept, we consider two interesting cases known in the literature as first- and second-order reactions. The former has a stretched exponential decay in time for its reagent concentration, and the latter evolves hyperbolically. We have established that the behavior can be explained by limit theorems of probability theory. The reaction evolution is directly connected with different behavior motivations in reagent populations. The reason for the universal kinetics is found in the indices of the corresponding probability distribution functions. They are macroscopic parameters measured in chemical experiments. Such an approach allows ones to discover what happens with molecular populations in microscopic dynamics. PMID:23942846

  17. Competition between charge exchange and chemical reaction - The D2/+/ + H system

    NASA Technical Reports Server (NTRS)

    Preston, R. K.; Cross, R. J., Jr.

    1973-01-01

    Study of the special features of molecular charge exchange and its competition with chemical reaction in the case of the D2(+) + H system. The trajectory surface hopping (TSH) model proposed by Tully and Preston (1971) is used to study this competition for a number of reactions involving the above system. The diatomics-in-molecules zero-overlap approximation is used to calculate the three adiabatic surfaces - one triplet and two singlet - which are needed to describe this system. One of the significant results of this study is that the chemical reaction and charge exchange are strongly coupled. It is also found that the number of trajectories passing into the chemical regions of the three surfaces depends very strongly on the surface crossings.-

  18. The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research

    SciTech Connect

    Westbrook, C K; Pitz, W J; Curran, H J; Mehl, M

    2008-07-16

    Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

  19. The US Export-Import Bank: No evidence of financing restricted chemical exports to Iraq

    SciTech Connect

    Mendelowitz, A.I.; Watson, J.E.; Wood, S.E.; Logan, D.L.; Hinojosa, S.L.

    1991-09-01

    The authors have reviewed U.S. Export-Import Bank (Eximbank) transactions involving chemicals exported to Iraq from January 1987 to August 1990. Specifically, the authors examined (1) whether there was any evidence that the Eximbank financed the export of dual-use chemicals to Iraq and (2) what the Eximbank`s role was in monitoring and controlling chemical exports. Results are based primarily on a review of documents provided to them by the Eximbank. They did not verify the Eximbank data or corroborate it with the records of the banks or exporters involved in the transactions. There was no evidence in the documents they reviewed to suggest that the Eximbank financed the export of dual-use chemicals (chemicals with both commercial and military applications that could be used for chemical weapons) -- as defined by the Department of Commerce -- to Iraq between January 1987 and August 1990. There were approximately 190 transactions between Iraq and the Eximbank during this period. They focused their review on the eight transactions involving pesticides and related products. The Eximbank has no responsibility or authority for monitoring or controlling the export of chemicals or any other commodities: the Departments of Commerce and State and the US Customs Service share those responsibilities. Nevertheless, the Eximbank has recently developed specific procedures to review applications for financing chemical exports. However, such procedures were not in place when the Eximbank approved the applications for seven of eight pesticide transactions that occurred between January 1987 and August 1990.

  20. A partial-propensity formulation of the stochastic simulation algorithm for chemical reaction networks with delays

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Rajesh; Sbalzarini, Ivo F.

    2011-01-01

    Several real-world systems, such as gene expression networks in biological cells, contain coupled chemical reactions with a time delay between reaction initiation and completion. The non-Markovian kinetics of such reaction networks can be exactly simulated using the delay stochastic simulation algorithm (dSSA). The computational cost of dSSA scales with the total number of reactions in the network. We reduce this cost to scale at most with the smaller number of species by using the concept of partial reaction propensities. The resulting delay partial-propensity direct method (dPDM) is an exact dSSA formulation for well-stirred systems of coupled chemical reactions with delays. We detail dPDM and present a theoretical analysis of its computational cost. Furthermore, we demonstrate the implications of the theoretical cost analysis in two prototypical benchmark applications. The dPDM formulation is shown to be particularly efficient for strongly coupled reaction networks, where the number of reactions is much larger than the number of species.

  1. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    NASA Astrophysics Data System (ADS)

    Vorotilin, V. P.; Yanovskii, Yu. G.

    2015-07-01

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities-the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  2. Stereodynamics of chemical reactions: quasi-classical, quantum and mixed quantum-classical theories

    NASA Astrophysics Data System (ADS)

    Xu, Wenwu; Zhao, Guangjiu

    2012-04-01

    In this review, some benchmark works by Han and coworkers on the stereodynamics of typical chemical reactions, triatomic reactions H + D2, Cl + H2 and O + H2 and polyatomic reaction Cl+CH4/CD4, are presented by using the quasi-classical, quantum and mixed quantum-classical methods. The product alignment and orientation in these A+BC model reactions are discussed in detail. We have also compared our theoretical results with experimental measurements and demonstrated that our theoretical results are in good agreement with the experimental results. Quasi-classical trajectory (QCT) method ignores some quantum effects like the tunneling effect and zero-point energy. The quantum method will be very time-consuming. Moreover, the mixed quantum-classical method can take into account some quantum effects and hence is expected to be applicable to large systems and widely used in chemical stereodynamics studies.

  3. Simulation of Chemical Isomerization Reaction Dynamics on a NMR Quantum Simulator

    NASA Astrophysics Data System (ADS)

    Lu, Dawei; Xu, Nanyang; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng

    2011-07-01

    Quantum simulation can beat current classical computers with minimally a few tens of qubits. Here we report an experimental demonstration that a small nuclear-magnetic-resonance quantum simulator is already able to simulate the dynamics of a prototype laser-driven isomerization reaction using engineered quantum control pulses. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future.

  4. Force-activated reactivity switch in a bimolecular chemical reaction at the single molecule level

    NASA Astrophysics Data System (ADS)

    Szoszkiewicz, Robert; Garcia-Manyes, Sergi; Liang, Jian; Kuo, Tzu-Ling; Fernandez, Julio M.

    2010-03-01

    Mechanical force can deform the reacting molecules along a well-defined direction of the reaction coordinate. However, the effect of mechanical force on the free-energy surface that governs a chemical reaction is still largely unknown. The combination of protein engineering with single-molecule AFM force-clamp spectroscopy allows us to study the influence of mechanical force on the rate at which a protein disulfide bond is reduced by some reducing agents in a bimolecular substitution reaction (so-called SN2). We found that cleavage of a protein disulfide bond by hydroxide anions exhibits an abrupt reactivity ``switch'' at 500 pN, after which the accelerating effect of force on the rate of an SN2 chemical reaction greatly diminishes. We propose that an abrupt force-induced conformational change of the protein disulfide bond shifts its ground state, drastically changing its reactivity in SN2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule. References: Sergi Garcia-Manyes, Jian Liang, Robert Szoszkiewicz, Tzu-Ling Kuo and Julio M. Fernandez, Nature Chemistry, 1, 236-242, 2009.

  5. Modeling heat dissipation at the nanoscale: an embedding approach for chemical reaction dynamics on metal surfaces.

    PubMed

    Meyer, Jrg; Reuter, Karsten

    2014-04-25

    We present an embedding technique for metallic systems that makes it possible to model energy dissipation into substrate phonons during surface chemical reactions from first principles. The separation of chemical and elastic contributions to the interaction potential provides a quantitative description of both electronic and phononic band structure. Application to the dissociation of O2 at Pd(100) predicts translationally "hot" oxygen adsorbates as a consequence of the released adsorption energy (ca.?2.6?eV). This finding questions the instant thermalization of reaction enthalpies generally assumed in models of heterogeneous catalysis. PMID:24683061

  6. THE LIFETIME OF AEROSOLS IN AMBIENT AIR: CONSIDERATION OF THE EFFECTS OF SURFACTANTS AND CHEMICAL REACTIONS

    SciTech Connect

    Toossi, R.; Novakov, T.

    1984-04-01

    The relatively long lifetime of droplets in atmospheric haze and fog in comparison with similar droplets of pure water is attributed to the presence of a monolayer of surfactant film and to the accumulation Of soluble salts from chemical reactions. The lifetime of these droplets is a significant factor in the evaluation of the role of heterogeneous aqueous chemical reactions occurring in the troposphere. Several mechanisms of SO{sub 2} oxidation in the presence of liquid water are investigated. It is shown that soot-catalyzed oxidation of sulfur dioxide could be responsible for the high level of sulfate concentration observed in the coastal industrial areas.

  7. Reacting gas mixtures in the state-to-state approach: The chemical reaction rates

    SciTech Connect

    Kustova, Elena V.; Kremer, Gilberto M.

    2014-12-09

    In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N{sub 2} across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.

  8. Detection of Medically Important Candida Species by Absolute Quantitation Real-Time Polymerase Chain Reaction

    PubMed Central

    Than, Leslie Thian Lung; Chong, Pei Pei; Ng, Kee Peng; Seow, Heng Fong

    2014-01-01

    Background: The number of invasive candidiasis cases has risen especially with an increase in the number of immunosuppressed and immunocom promised patients. The early detection of Candida species which is specific and sensitive is important in determining the correct administration of antifungal drugs to patients. Objectives: This study aims to develop a method for the detection, identification and quantitation of medically important Candida species through quantitative polymerase chain reaction (qPCR). Materials and Methods: The isocitrate lyase (ICL) gene which is not found in mammals was chosen as the target gene of real-time PCR. Absolute quantitation of the gene copy number was achieved by constructing the plasmid containing the ICL gene which is used to generate standard curve. Twenty fungal species, two bacterial species and human DNA were tested to check the specificity of the detection method. Results: All eight Candida species were successfully detected, identified and quantitated based on the ICL gene. A seven-log range of the gene copy number and a minimum detection limit of 103 copies were achieved. Conclusions: A one-tube absolute quantification real-time PCR that differentiates medically important Candida species via individual unique melting temperature was achieved. Analytical sensitivity and specificity were not compromised. PMID:25789129

  9. Oxidation as an important factor of protein damage: Implications for Maillard reaction.

    PubMed

    Trnkova, L; Drsata, J; Bousova, I

    2015-06-01

    Protein oxidation, the process caused especially by reactive oxygen and nitrogen species, is thought to play a major role in various oxidative processes within cells and is implicated in the development of many human diseases. This review provides a brief overview of the protein oxidation with the emphasis on the types of oxidation (oxidation of protein backbone and amino acid residues side chains, site-specific metal-catalysed protein oxidation), oxidationdependent generation of protein hydroperoxides, carbonyl derivatives and protein-protein cross-linkages. Nonenzymatic glycoxidation (also known as Maillard reaction) as an important factor of protein damage, consequences of oxidative protein impairment and related diseases as well as means of monitoring and assessment of protein modifications are discussed. PMID:25963268

  10. Characterization of Chemically Modified Hyperthermophilic Enzymes for Chemical Syntheses and Bioremediation Reactions

    SciTech Connect

    Davison, Brian H.; Adams, Michael

    1999-06-01

    Remediation processes frequently involve species possessing limited solubility in water. We are interested in novel strategies that use molecularly modified enzymes with enhanced activity and stability for the remediation of recalcitrant compounds in organic solvents. The performance of naturally-occurring enzymes is usually quite limited in such organic environments. The primary objective of the current work is to gain a fundamental understanding of the molecular and catalytic properties of enzymes that have been chemically modified so that they are catalytically active and chemically-stable in organic solvents. The premise for this study is that stabilized and activated enzymes, which can function at hash chemical conditions, are optimally suited for bioremediation in nonaqueous media where substrates of interest are more soluble and processed with greater efficiency. This unique strategy is examined with respect to the degradation of chlorophenols and PCBs.

  11. Ion-Molecule Reactions and Chemical Composition of Emanated from Herculane Spa Geothermal Sources

    PubMed Central

    Cosma, Constantin; Suciu, Ioan; Jntschi, Lorentz; Bolboac?, Sorana D.

    2008-01-01

    The paper presents a chemical composition analysis of the gases emanated from geothermal sources in the Herculane Spa area (Romania). The upper homologues of methane have been identified in these gases. An ion-molecule reaction mechanism could be implicated in the formation of the upper homologues of methane. The CH4+ ions that appear under the action of radiation are the starting point of these reactions. The presence of hydrogen in the emanated gases may be also a result of these reactions. PMID:19325844

  12. Homodyne High-Harmonic Spectroscopy: Coherent Imaging of a Unimolecular Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Beaudoin Bertrand, Julien

    At the heart of high harmonic generation lies a combination of optical and collision physics entwined by a strong laser field. An electron, initially tunnel-ionized by the field, driven away then back in the continuum, finally recombines back to rest in its initial ground state via a radiative transition. The emitted attosecond (atto=10-18) XUV light pulse carries all the information (polarization, amplitude and phase) about the photorecombination continuum-to-ground transition dipolar field. Photorecombination is related to the time-reversed photoionization process. In this perspective, high-harmonic spectroscopy extends well-established photoelectron spectroscopy, based on charged particle detection, to a fully coherent one, based on light characterization. The main achievement presented in this thesis is to use high harmonic generation to probe femtosecond (femto=10-15) chemical dynamics for the first time. Thanks to the coherence imposed by the strong driving laser field, homodyne detection of attosecond pulses from excited molecules undergoing dynamics is achieved, the signal from unexcited molecules acting as the reference local oscillator. First, applying time-resolved high-harmonic spectroscopy to the photodissociation of a diatomic molecule, Br2 ? Br + Br, allows us to follow the break of a chemical bond occurring in a few hundreds of femtoseconds. Second, extending it to a triatomic (NO2) lets us observe both the previously unseen (but predicted) early femtosecond conical intersection dynamics followed by the late picosecond statistical photodissociation taking place in the reaction NO2 ? NO + O. Another important realization of this thesis is the development of a complementary technique to time-resolved high-harmonic spectroscopy called LAPIN, for Linked Attosecond Phase INterferometry. When combined together, time-resolved high-harmonic spectroscopy and LAPIN give access to the complex photorecombination dipole of aligned excited molecules. These achievements lay the basis for electron recollision tomographic imaging of a chemical reaction with unprecedented angstrom (1 angstrom= 0.1 nanometer) spatial resolution. Other contributions dedicated to the development of attosecond science and the generalization of high-harmonic spectroscopy as a novel, fully coherent molecular spectroscopy will also be presented in this thesis.

  13. O/S-1/ interactions - The product channels. [collisional electron quenching and chemical reaction pathway frequencies

    NASA Technical Reports Server (NTRS)

    Slanger, T. G.; Black, G.

    1978-01-01

    The first measurements are reported of the reaction pathways for the interaction between oxygen atoms in the 4.19 eV S-1 state, and four molecules, N2O, CO2, H2O, and NO. Distinction is made between three possible paths - quenching to O(D-1), quenching to O(P-3), and chemical reaction. With N2O, the most reasonable interpretation of the data indicates that there no reaction, in sharp contrast with the interaction between O(D-1) and N2O, which proceeds entirely by reaction. Similarly, there is no reaction with CO2. With H2O, the reactive pathway is the dominant one, although electronic quenching is not negligible. With NO, O(D-1) is the preferred product.

  14. 15 CFR 713.3 - Annual declaration and reporting requirements for exports and imports of Schedule 2 chemicals.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... requirements for exports and imports of Schedule 2 chemicals. 713.3 Section 713.3 Commerce and Foreign Trade... declaration and reporting requirements for exports and imports of Schedule 2 chemicals. (a) Declarations and reports of exports and imports of Schedule 2 chemicals(1) Declarations. A Schedule 2 plant site that...

  15. Conversion process of chemical reaction into mechanical work through solvation change

    NASA Astrophysics Data System (ADS)

    Tokunaga, Ken; Furumi, Takuya; Akiyama, Ryo

    2011-03-01

    Many systems in which the hydrolysis of ATP is finally converted into the mechanical work are known (e.g. actin-myosin motor protein system). It seems that there are various types of the conversion mechanism. In this work, we examined a possibility of conversion from chemical reaction into mechanical work due to solvation change around the reaction site by using the molecular dynamics simulation (MD) with explicit solvent model. In our model, solvent molecules, S, and a motor (colloidal particle), M, are treated as Lennard-Jones (LJ) particles. Effect of chemical reaction is taken in the system as the change of LJ potential parameter e between S and M, however the reaction site is restricted on the M. The parameter ? is switched to ?' = 1000 ? during the reaction (?t), Fig. (a). Averaged displacement of the motor M is shown in Fig. (b). The motor M is driven by this reaction model, however the direction and efficiency are dependent on the reaction time ?t and the thermodynamic state of the solvent.

  16. Charge exchange and chemical reactions with trapped Th{sup 3+}

    SciTech Connect

    Churchill, L. R.; DePalatis, M. V.; Chapman, M. S.

    2011-01-15

    We have measured the reaction rates of trapped, buffer gas cooled Th{sup 3+} and various gases and have analyzed the reaction products using trapped ion mass spectrometry techniques. Ion trap lifetimes are usually limited by reactions with background molecules, and the high electron affinity of multiply charged ions such as Th{sup 3+} make them more prone to loss. Our results show that reactions of Th{sup 3+} with carbon dioxide, methane, and oxygen all occur near the classical Langevin rate, while reaction rates with argon, hydrogen, and nitrogen are orders of magnitude lower. Reactions of Th{sup 3+} with oxygen and methane proceed primarily via charge exchange, while simultaneous charge exchange and chemical reaction occurs between Th{sup 3+} and carbon dioxide. Loss rates of Th{sup 3+} in helium are consistent with reaction with impurities in the gas. Reaction rates of Th{sup 3+} with nitrogen and argon depend on the internal electronic configuration of the Th{sup 3+}.

  17. Chemical Kinetic Reaction Mechanisms for Combustion of Hydrocarbon and Other Types of Chemical Fuels

    DOE Data Explorer

    Reaction mechanisms have been tested and validated extensively through comparisons between computed results and measured data from laboratory experiments (e.g., shock tubes, laminar flames, rapid compression machines, flow reactors, stirred reactors) and from practical systems (e.g., diesel engines, spark-ignition engines, homogeneous charge, compression ignition (HCCI) engines). These kinetic models are used to examine a wide range of combustion systems.

  18. Turkish, Indian, and American Chemistry Textbooks Use of Inscriptions to Represent "Types of Chemical Reactions"

    ERIC Educational Resources Information Center

    Aydin, Sevgi; Sinha, Somnath; Izci, Kemal; Volkmann, Mark

    2014-01-01

    The purpose of this study was to investigate inscriptions used in "Types of Chemical Reactions" topic in Turkish, Indian, and American chemistry textbooks. We investigated both the types of inscriptions and how they were used in textbooks to support learning. A conceptual analysis method was employed to determine how those textbooks use

  19. The Effective Concepts on Students' Understanding of Chemical Reactions and Energy

    ERIC Educational Resources Information Center

    Ayyildiz, Yildizay; Tarhan, Leman

    2012-01-01

    The purpose of this study was to determine the relationship between the basic concepts related to the unit of "Chemical Reactions and Energy" and the sub-concepts underlying for meaningful learning of the unit and to investigate the effectiveness of them on students' learning achievements. For this purpose, the basic concepts of the unit were

  20. Eliciting Students' Understandings of Chemical Reactions Using Two Forms of Essay Questions during a Learning Cycle.

    ERIC Educational Resources Information Center

    Cavallo, Ann M. L.; McNeely, Jack C.; Marek, Edmund A.

    2003-01-01

    Examines 9th grade students' explanations of chemical reactions using two forms of open-ended essay questions, those providing students with key terms to be used as "anchors" on which to base their essay, and those that do not provide terms. Results indicate that more misunderstandings were elicited by the use of key terms as compared to the

  1. Facilitating High School Students' Use of Multiple Representations to Describe and Explain Simple Chemical Reactions

    ERIC Educational Resources Information Center

    Chandrasegaran, A. L.; Treagust, David F.; Mocerino, Mauro

    2011-01-01

    This study involved the evaluation of the efficacy of a planned instructional program to facilitate understanding of the macroscopic, submicroscopic and symbolic representational systems when describing and explaining chemical reactions by sixty-five Grade 9 students in a Singapore secondary school. A two-tier multiple-choice diagnostic instrument

  2. Effectiveness of Conceptual Change Text-Oriented Instruction on Students' Understanding of Energy in Chemical Reactions

    ERIC Educational Resources Information Center

    Tastan, Ozgecan; Yalcinkaya, Eylem; Boz, Yezdan

    2008-01-01

    The aim of this study is to compare the effectiveness of conceptual change text instruction (CCT) in the context of energy in chemical reactions. The subjects of the study were 60, 10th grade students at a high school, who were in two different classes and taught by the same teacher. One of the classes was randomly selected as the experimental

  3. Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes

    ERIC Educational Resources Information Center

    Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

    2014-01-01

    In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge,

  4. Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow

    ERIC Educational Resources Information Center

    Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan

    2012-01-01

    In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms

  5. The Effective Concepts on Students' Understanding of Chemical Reactions and Energy

    ERIC Educational Resources Information Center

    Ayyildiz, Yildizay; Tarhan, Leman

    2012-01-01

    The purpose of this study was to determine the relationship between the basic concepts related to the unit of "Chemical Reactions and Energy" and the sub-concepts underlying for meaningful learning of the unit and to investigate the effectiveness of them on students' learning achievements. For this purpose, the basic concepts of the unit were…

  6. Turkish, Indian, and American Chemistry Textbooks Use of Inscriptions to Represent "Types of Chemical Reactions"

    ERIC Educational Resources Information Center

    Aydin, Sevgi; Sinha, Somnath; Izci, Kemal; Volkmann, Mark

    2014-01-01

    The purpose of this study was to investigate inscriptions used in "Types of Chemical Reactions" topic in Turkish, Indian, and American chemistry textbooks. We investigated both the types of inscriptions and how they were used in textbooks to support learning. A conceptual analysis method was employed to determine how those textbooks use…

  7. Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes

    ERIC Educational Resources Information Center

    Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

    2014-01-01

    In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge,…

  8. Facilitating High School Students' Use of Multiple Representations to Describe and Explain Simple Chemical Reactions

    ERIC Educational Resources Information Center

    Chandrasegaran, A. L.; Treagust, David F.; Mocerino, Mauro

    2011-01-01

    This study involved the evaluation of the efficacy of a planned instructional program to facilitate understanding of the macroscopic, submicroscopic and symbolic representational systems when describing and explaining chemical reactions by sixty-five Grade 9 students in a Singapore secondary school. A two-tier multiple-choice diagnostic instrument…

  9. Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow

    ERIC Educational Resources Information Center

    Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan

    2012-01-01

    In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms…

  10. Chemical equilibrium and reaction modeling of arsenic and selenium in soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The chemical processes and soil factors that affect the concentrations of As and Se in soil solution were discussed. Both elements occur in two redox states differing in toxicity and reactivity. Methylation and volatilization reactions occur in soils and can act as detoxification pathways. Precip...

  11. DEVELOPMENT AND TESTING OF A SURROGATE SPECIES CHEMICAL REACTION MECHANISM. VOLUME 2

    EPA Science Inventory

    A photochemical reaction mechanism has been updated and extensively evaluated. The testing and refinement of the surrogate species mechanism was performed in order to create an improved chemical mechanism for the atmospheric simulation models that are used to develop ozone contro...

  12. DEVELOPMENT AND TESTING OF A SURROGATE SPECIES CHEMICAL REACTION MECHANISM. VOLUME 1

    EPA Science Inventory

    A photochemical reaction mechanism has been updated and extensively evaluated. The testing and refinement of the surrogate species mechanism was performed in order to create an improved chemical mechanism for the atmospheric simulation models that are used to develop ozone contro...

  13. Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction

    ERIC Educational Resources Information Center

    Sobel, Sabrina G.; Cohen, Skyler

    2010-01-01

    Surprisingly, spectator ions are responsible for unexpected kinetics in the biphasic copper(II)-aluminum displacement reaction, with the rate of reaction dependent on the identity of the otherwise ignored spectator ions. Application of a published kinetic analysis developed for a reaction between a rotating Al disk and a Cu(II) ion solution to the

  14. Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction

    ERIC Educational Resources Information Center

    Sobel, Sabrina G.; Cohen, Skyler

    2010-01-01

    Surprisingly, spectator ions are responsible for unexpected kinetics in the biphasic copper(II)-aluminum displacement reaction, with the rate of reaction dependent on the identity of the otherwise ignored spectator ions. Application of a published kinetic analysis developed for a reaction between a rotating Al disk and a Cu(II) ion solution to the…

  15. On chemical reactions in the laser-induced breakdown of a liquid

    NASA Astrophysics Data System (ADS)

    Margulis, M. A.; Ovchinnikov, O. B.; Margulis, I. M.

    2006-06-01

    It is shown experimentally that a laser-induced breakdown of a liquid is accompanied by chemical reactions initiated by radicals and excited species formed in the spark. It is found that, in water, the laser-induced breakdown is accompanied by the dissociation of water and dissolved nitrogen molecules with the formation of HNO2 and HNO3, while, in a FeSO4 aqueous solution, by the Fe2+ ? Fe3+ oxidation reaction. It is assumed that the mechanism of the process is analogous to that of the action of ionizing radiations and the chemical action of ultrasonically induced cavitation (it is proposed that this mechanism of chemical action of a laser-induced spark proposed be termed indirect). Energy yields of these reactions are found to be of the same order of magnitude as for sonochemical redox reactions. It is shown that the laser-induced breakdown of an aqueous solution of maleic acid is accompanied by its stereoisomerization into fumaric acid, a process catalyzed by small amounts of an alkyl bromide. It is established that, for the formation of fumaric acid in a laser-induced spark, the energy yield is about five orders of magnitude higher than that typical of the above-mentioned redox reactions in the laser-induced spark.

  16. Studies in photochemical smog chemistry. I. Atmospheric chemistry of toluene. II. Analysis of chemical reaction mechanisms for photochemical smog

    SciTech Connect

    Leone, J.A.

    1985-01-01

    This study focuses on two related topics in the gas phase organic chemistry of importance in urban air pollution. Part I describes an experimental and modeling effort aimed at developing a new explicit reaction mechanism for the atmospheric photooxidation of toluene. This mechanism is tested using experimental data from both indoor and outdoor smog chamber facilities. The predictions of the new reaction mechanism are found to be in good agreement with both sets of experimental data. Additional simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where the understanding is not complete. The outdoor experimental facility, which was built to provide the second set of experimental data, consists of a 65 cubic meter teflon smog chamber together with full instrumentation capable of measuring ozone, nitrogen dioxide, nitric oxide, peroxyacetyl nitrate (PAN), carbon monoxide, relative humidity, temperature, aerosol size distributions, and of course toluene and its photooxidation products. In Part II, a theoretical analysis of lumped chemical reaction mechanisms for photochemical smog is presented. Included is a description of a new counter species analysis technique which can be used to analyze any complex chemical reaction mechanism. Finally, a new lumped mechanism for photochemical smog is developed and tested against experimental data from two smog chamber facilities. Advantages of this mechanism relative to the existing lumped mechanisms are discussed.

  17. Child-Rearing Practices toward Children with Hemophilia: The Relative Importance of Clinical Characteristics and Parental Emotional Reactions.

    ERIC Educational Resources Information Center

    Banis, S.; Suurmeijer, Th. P. B. M.; van Peer, D. R.

    1999-01-01

    Addresses the relative importance of clinical characteristics of the child and parental emotional reactions, to child-rearing practices towards children with hemophilia. Results indicate that mother's emotional reactions appear to have a stronger influence on child-rearing uncertainty and overprotection than clinical characteristics of the child.

  18. Child-Rearing Practices toward Children with Hemophilia: The Relative Importance of Clinical Characteristics and Parental Emotional Reactions.

    ERIC Educational Resources Information Center

    Banis, S.; Suurmeijer, Th. P. B. M.; van Peer, D. R.

    1999-01-01

    Addresses the relative importance of clinical characteristics of the child and parental emotional reactions, to child-rearing practices towards children with hemophilia. Results indicate that mother's emotional reactions appear to have a stronger influence on child-rearing uncertainty and overprotection than clinical characteristics of the child.…

  19. Proposed chemical mechanisms leading to secondary organic aerosol in the reactions of aliphatic amines with hydroxyl and nitrate radicals

    NASA Astrophysics Data System (ADS)

    Price, Derek J.; Clark, Christopher H.; Tang, Xiaochen; Cocker, David R.; Purvis-Roberts, Kathleen L.; Silva, Philip J.

    2014-10-01

    The presence and importance of amines in the atmosphere, including aliphatic amines, continues to gain more attention. The atmospheric reaction mechanisms of these amines with key atmospheric radicals are important to predict both daytime and nighttime atmospheric chemistry. While previous studies have focused on the production of amine salts, this analysis looks at the importance of peroxy radical reactions to the formation of secondary organic aerosol. Atmospheric oxidation mechanisms are presented to explain the observed chemistry. A series of environmental chamber experiments were conducted in which aliphatic tertiary and secondary amines were reacted with either hydroxyl radical (OH) or nitrate radical (NO3). Chemical composition of the aerosol products was obtained with a High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Particle Into Liquid Sampler Time of Flight Mass Spectrometer (PILS-ToF-MS), while the chemical composition of the gas-phase products was obtained with a Selected Ion Flow Tube Mass Spectrometer (SIFT-MS). A number of aerosol-phase mass spectra showed highly oxidized fragments at a much higher molecular weight (MW) than the amine precursor. It is proposed that these larger compounds are oligomers formed through peroxy radical reactions with hydrogen rearrangement. Another reaction pathway observed was the formation of amine salts. The relative importance of each pathway to the overall production of aerosol is found to be dependent on the type of amine and oxidant. For example, the oligomers were observed in the tertiary methyl amines, while the formation of amine salts was more prevalent in the secondary and tertiary ethyl amines.

  20. Spatiotemporal regulation of chemical reaction kinetics of cell surface molecules by active remodeling of cortical actin

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Bhaswati; Chaudhuri, Abhishek; Gowrishankar, Kripa; Mayor, Satyajit; Rao, Madan

    2010-03-01

    Cell surface proteins such as lipid tethered GPI-anchored proteins and Ras-proteins are distributed as monomers and nanoclusters on the surface of living cells. Recent work from our laboratory suggests that the spatial distribution and dynamics of formation and breakup of these nanoclusters is controlled by the active remodeling dynamics of the underlying cortical actin. To explain these observations, we propose a novel mechanism of nanoclustering, involving the transient binding to and advection along constitutively occuring ``asters'' of cortical actin. Here we study the consequences of such active actin based clustering, in the context of chemical reactions involving conformational changes of cell surface proteins. We find that active remodeling of cortical actin, can give rise to a dramatic increase in the reaction efficiency and output levels. In general, such actin driven clustering of membrane proteins could be a cellular mechanism to spatiotemporally regulate and amplify local chemical reaction rates, in the context of signalling and endocytosis.

  1. On a theory of stability for nonlinear stochastic chemical reaction networks

    SciTech Connect

    Smadbeck, Patrick; Kaznessis, Yiannis N.

    2015-05-14

    We present elements of a stability theory for small, stochastic, nonlinear chemical reaction networks. Steady state probability distributions are computed with zero-information (ZI) closure, a closure algorithm that solves chemical master equations of small arbitrary nonlinear reactions. Stochastic models can be linearized around the steady state with ZI-closure, and the eigenvalues of the Jacobian matrix can be readily computed. Eigenvalues govern the relaxation of fluctuation autocorrelation functions at steady state. Autocorrelation functions reveal the time scales of phenomena underlying the dynamics of nonlinear reaction networks. In accord with the fluctuation-dissipation theorem, these functions are found to be congruent to response functions to small perturbations. Significant differences are observed in the stability of nonlinear reacting systems between deterministic and stochastic modeling formalisms.

  2. Stability of a laminar premixed supersonic free shear layer with chemical reactions

    NASA Technical Reports Server (NTRS)

    Menon, S.; Anderson, J. D., Jr.; Pai, S. I.

    1984-01-01

    The stability of a two-dimensional compressible supersonic flow in the wake of a flat plate is discussed. The fluid is a multi-species mixture which is undergoing finite rate chemical reactions. The spatial stability of an infinitesimal disturbance in the fluid is considered. Numerical solutions of the eigenvalue stability equations for both reactive and nonreactive supersonic flows are presented and discussed. The chemical reactions have significant influence on the stability behavior. For instance, a neutral eigenvalue is observed near the freestream Mach number of 2.375 for the nonreactive case, but disappears when the reaction is turned on. For reactive flows, the eigenvalues are not very dependent on the free stream Mach number.

  3. A Spectroscopist's View of Energy States, Energy Transfers, and Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Moore, C. Bradley

    2007-05-01

    This chapter describes a research career beginning at Berkeley in 1960, shortly after Sputnik and the invention of the laser. Following thesis work on vibrational spectroscopy and the chemical reactivity of small molecules, we studied vibrational energy transfers in my own lab. Collision-induced transfers among vibrations of a single molecule, from one molecule to another, and from vibration to rotation and translation were elucidated. My research group also studied the competition between vibrational relaxation and chemical reaction for potentially reactive collisions with one molecule vibrationally excited. Lasers were used to enrich isotopes by the excitation of a predissociative transition of a selected isotopomer. We also tested the hypotheses of transition-state theory for unimolecular reactions of ketene, formaldehyde, and formyl fluoride by (a) resolving individual molecular eigenstates above a dissociation threshold, (b) locating vibrational levels at the transition state, (c) observing quantum resonances in the barrier region for motion along a reaction coordinate, and (d) studying energy release to fragments.

  4. On a theory of stability for nonlinear stochastic chemical reaction networks

    PubMed Central

    Smadbeck, Patrick; Kaznessis, Yiannis N.

    2015-01-01

    We present elements of a stability theory for small, stochastic, nonlinear chemical reaction networks. Steady state probability distributions are computed with zero-information (ZI) closure, a closure algorithm that solves chemical master equations of small arbitrary nonlinear reactions. Stochastic models can be linearized around the steady state with ZI-closure, and the eigenvalues of the Jacobian matrix can be readily computed. Eigenvalues govern the relaxation of fluctuation autocorrelation functions at steady state. Autocorrelation functions reveal the time scales of phenomena underlying the dynamics of nonlinear reaction networks. In accord with the fluctuation-dissipation theorem, these functions are found to be congruent to response functions to small perturbations. Significant differences are observed in the stability of nonlinear reacting systems between deterministic and stochastic modeling formalisms. PMID:25978877

  5. Modeling pore collapse and chemical reactions in shock-loaded HMX crystals

    NASA Astrophysics Data System (ADS)

    Austin, R. A.; Barton, N. R.; Howard, W. M.; Fried, L. E.

    2014-05-01

    The localization of deformation in shock-loaded crystals of high explosive material leads to the formation of hot spots, which, if hot enough, initiate chemical reactions. The collapse of microscopic pores contained within a crystal is one such process that localizes energy and generates hot spots. Given the difficulty of resolving the details of pore collapse in shock compression experiments, it is useful to study the problem using direct numerical simulation. In this work, we focus on simulating the shock-induced closure of a single pore in crystalline β-HMX using a multiphysics finite element code. To address coupled thermal-mechanical-chemical responses, the model incorporates a crystal-mechanics-based description of thermoelasto-viscoplasticity, the crystal melting behavior, and transformation kinetics for a single-step decomposition reaction. The model is applied to stress wave amplitudes of up to 11 GPa to study the details of pore collapse, energy localization, and the early stages of reaction initiation.

  6. Organo- and nano-catalyst in greener reaction medium: Microwave-assisted expedient synthesis of fine chemicals

    EPA Science Inventory

    The use of emerging microwave (MW) -assisted chemistry techniques is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. A brief account of our experiences in developing MW-assisted organic transformations, which invo...

  7. Chemical reactions in TEOS/ozone chemical vapor deposition[TetraEthylOrtho Silicate

    SciTech Connect

    HO,PAULINE

    2000-02-01

    A reaction mechanism for TEOS/O{sub 3} CVD in a SVG/WJ atmospheric pressure furnace belt reactor has been developed and calibrated with experimental deposition rate data. One-dimensional simulations using this mechanism successfully reproduce the trends observed in a set of 31 experimental runs in a WJ-TEOS999 reactor. Two-dimensional simulations using this mechanism successfully reproduce the average deposition rates for 3 different experimental conditions in a WJ-1500TF reactor, although the deposition profiles predicted by the model are flatter than the experimental static prints.

  8. Looking for chemical reaction networks exhibiting a drift along a manifold of marginally stable states.

    PubMed

    Brogioli, Doriano

    2013-02-01

    I recently reported some examples of mass-action equations that have a continuous manifold of marginally stable stationary states [Brogioli, D., 2010. Marginally stable chemical systems as precursors of life. Phys. Rev. Lett. 105, 058102; Brogioli, D., 2011. Marginal stability in chemical systems and its relevance in the origin of life. Phys. Rev. E 84, 031931]. The corresponding chemical reaction networks show nonclassical effects, i.e. a violation of the mass-action equations, under the effect of the concentration fluctuations: the chemical system drifts along the marginally stable states. I proposed that this effect is potentially involved in abiogenesis. In the present paper, I analyze the mathematical properties of mass-action equations of marginally stable chemical reaction networks. The marginal stability implies that the mass-action equations obey some conservation law; I show that the mathematical properties of the conserved quantity characterize the motion along the marginally stable stationary state manifold, i.e. they allow to predict if the fluctuations give rise to a random walk or a drift under the effect of concentration fluctuations. Moreover, I show that the presence of the drift along the manifold of marginally stable stationary-states is a critical property, i.e. at least one of the reaction constants must be fine tuned in order to obtain the drift. PMID:23160143

  9. Progress toward chemical accuracy in the computer simulation of condensed phase reactions.

    PubMed Central

    Bash, P A; Ho, L L; MacKerell, A D; Levine, D; Hallstrom, P

    1996-01-01

    We describe a procedure for the generation of chemically accurate computer-simulation models to study chemical reactions in the condensed phase. The process involves (i) the use of a coupled semiempirical quantum and classical molecular mechanics method to represent solutes and solvent, respectively; (ii) the optimization of semiempirical quantum mechanics (QM) parameters to produce a computationally efficient and chemically accurate QM model; (iii) the calibration of a quantum/classical microsolvation model using ab initio quantum theory; and (iv) the use of statistical mechanical principles and methods to simulate, on massively parallel computers, the thermodynamic properties of chemical reactions in aqueous solution. The utility of this process is demonstrated by the calculation of the enthalpy of reaction in vacuum and free energy change in aqueous solution for a proton transfer involving methanol, methoxide, imidazole, and imidazolium, which are functional groups involved with proton transfers in many biochemical systems. An optimized semiempirical QM model is produced, which results in the calculation of heats of formation of the above chemical species to within 1.0 kcal/mol (1 kcal = 4.18 kJ) of experimental values. The use of the calibrated QM and microsolvation QM/MM (molecular mechanics) models for the simulation of a proton transfer in aqueous solution gives a calculated free energy that is within 1.0 kcal/mol (12.2 calculated vs. 12.8 experimental) of a value estimated from experimental pKa values of the reacting species. PMID:11607654

  10. Calculation of total free energy yield as an alternative approach for predicting the importance of potential chemolithotrophic reactions in geothermal springs.

    PubMed

    Dodsworth, Jeremy A; McDonald, Austin I; Hedlund, Brian P

    2012-08-01

    To inform hypotheses regarding the relative importance of chemolithotrophic metabolisms in geothermal environments, we calculated free energy yields of 26 chemical reactions potentially supporting chemolithotrophy in two US Great Basin hot springs, taking into account the effects of changing reactant and product activities on the Gibbs free energy as each reaction progressed. Results ranged from 1.2 × 10(-5) to 3.6 J kg(-1) spring water, or 3.7 × 10(-5) to 11.5 J s(-1) based on measured flow rates, with aerobic oxidation of CH(4) or NH4 + giving the highest average yields. Energy yields calculated without constraining pH were similar to those at constant pH except for reactions where H(+) was consumed, which often had significantly lower yields when pH was unconstrained. In contrast to the commonly used normalization of reaction chemical affinities per mole of electrons transferred, reaction energy yields for a given oxidant varied by several orders of magnitude and were more sensitive to differences in the activities of products and reactants. The high energy yield of aerobic ammonia oxidation is consistent with previous observations of significant ammonia oxidation rates and abundant ammonia-oxidizing archaea in sediments of these springs. This approach offers an additional lens through which to view the thermodynamic landscape of geothermal springs. PMID:22443686

  11. Chemical kinetic analysis of hydrogen-air ignition and reaction times

    NASA Technical Reports Server (NTRS)

    Rogers, R. C.; Schexnayder, C. J., Jr.

    1981-01-01

    An anaytical study of hydrogen air kinetics was performed. Calculations were made over a range of pressure from 0.2 to 4.0 atm, temperatures from 850 to 2000 K, and mixture equivalence ratios from 0.2 to 2.0. The finite rate chemistry model included 60 reactions in 20 species of the H2-O2-N2 system. The calculations also included an assessment of how small amounts of the chemicals H2O, NOx, H2O2, and O3 in the initial mixture affect ignition and reaction times, and how the variation of the third body efficiency of H2O relative of N2 in certain key reactions may affect reaction time. The results indicate that for mixture equivalence ratios between 0.5 and 1.7, ignition times are nearly constant; however, the presence of H2O and NO can have significant effects on ignition times, depending on the mixture temperature. Reaction time is dominantly influenced by pressure but is nearly independent of initial temperature, equivalence ratio, and the addition of chemicals. Effects of kinetics on reaction at supersonic combustor conditions are discussed.

  12. The Quantum-Kinetic Chemical Reaction Model for Navier-Stokes Codes

    NASA Astrophysics Data System (ADS)

    Gallis, Michael A.; Wagnild, Ross M.; Torczynski, John R.

    2013-11-01

    The Quantum-Kinetic chemical reaction model of Bird is formulated as a non-equilibrium chemical reaction model for Navier-Stokes codes. The model is based solely on thermophysical, molecular-level information and is capable of reproducing measured equilibrium reaction rates without using any experimentally measured reaction-rate information. The model recognizes the principal role of vibrational energy in overcoming the reaction energy threshold. The effect of rotational non-equilibrium is introduced as a perturbation to the effect of vibrational non-equilibrium. Since the model uses only molecular-level properties, it is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. This ability is demonstrated in the context of both Navier-Stokes and DSMC codes. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  13. The addition reaction between silylene and ethyne: further isotope studies, pressure dependence studies, and quantum chemical calculations.

    PubMed

    Becerra, Rosa; Cannady, J Pat; Dormer, Guy; Walsh, Robin

    2008-09-18

    Time-resolved kinetic studies of the reaction of dideutero-silylene, SiD 2, generated by laser flash photolysis of phenylsilane-d 3, have been carried out to obtain rate constants for its bimolecular reaction with C 2H 2. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF 6 bath gas, at five temperatures in the range 297-600 K. The second-order rate constants obtained by extrapolation to the high-pressure limits at each temperature fitted the Arrhenius equation log( k (infinity)/cm (3) molecule (-1) s (-1)) = (-10.05 +/- 0.05) + (3.43 +/- 0.36 kJ mol (-1))/ RT ln 10. The rate constants were used to obtain a comprehensive set of isotope effects by comparison with earlier obtained rate constants for the reactions of SiH 2 with C 2H 2 and C 2D 2. Additionally, pressure-dependent rate constants for the reaction of SiH 2 with C 2H 2 in the presence of He (1-100 Torr) were obtained at 300, 399, and 613 K. Quantum chemical (ab initio) calculations of the SiC 2H 4 reaction system at the G3 level support the initial formation of silirene, which rapidly isomerizes to ethynylsilane as the major pathway. Reversible formation of vinylsilylene is also an important process. The calculations also indicate the involvement of several other intermediates, not previously suggested in the mechanism. RRKM calculations are in semiquantitative agreement with the pressure dependences and isotope effects suggested by the ab initio calculations, but residual discrepancies suggest the possible involvement of the minor reaction channel, SiH 2 + C 2H 2 --> Si( (3)P 1) + C 2H 4. The results are compared and contrasted with previous studies of this reaction system. PMID:18714973

  14. General chemical kinetics computer program for static and flow reactions, with application to combustion and shock-tube kinetics

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    A general chemical kinetics program is described for complex, homogeneous ideal-gas reactions in any chemical system. Its main features are flexibility and convenience in treating many different reaction conditions. The program solves numerically the differential equations describing complex reaction in either a static system or one-dimensional inviscid flow. Applications include ignition and combustion, shock wave reactions, and general reactions in a flowing or static system. An implicit numerical solution method is used which works efficiently for the extreme conditions of a very slow or a very fast reaction. The theory is described, and the computer program and users' manual are included.

  15. Exchange repulsive potential adaptable for electronic structure changes during chemical reactions

    NASA Astrophysics Data System (ADS)

    Yokogawa, D.

    2015-04-01

    Hybrid methods combining quantum mechanical (QM) and classical calculations are becoming important tools in chemistry. The popular approach to calculate the interaction between QM and classical calculations employs interatomic potentials. In most cases, the interatomic potential is constructed of an electrostatic (ES) potential and a non-ES potential. Because QM treatment is employed in the calculation of the ES potential, the electronic change can be considered in this ES potential. However, QM treatment of the non-ES potential is difficult because of high computational cost. To overcome this difficulty of evaluating the non-ES potential, we proposed an exchange repulsive potential as the main part of the non-ES potential on the basis of a QM approach. This potential is independent of empirical parameters and adaptable for electronic structure. We combined this potential with the reference interaction site model self-consistent field explicitly including spatial electron density distribution and successfully applied it to the chemical reactions in aqueous phase.

  16. Exchange repulsive potential adaptable for electronic structure changes during chemical reactions

    SciTech Connect

    Yokogawa, D.

    2015-04-28

    Hybrid methods combining quantum mechanical (QM) and classical calculations are becoming important tools in chemistry. The popular approach to calculate the interaction between QM and classical calculations employs interatomic potentials. In most cases, the interatomic potential is constructed of an electrostatic (ES) potential and a non-ES potential. Because QM treatment is employed in the calculation of the ES potential, the electronic change can be considered in this ES potential. However, QM treatment of the non-ES potential is difficult because of high computational cost. To overcome this difficulty of evaluating the non-ES potential, we proposed an exchange repulsive potential as the main part of the non-ES potential on the basis of a QM approach. This potential is independent of empirical parameters and adaptable for electronic structure. We combined this potential with the reference interaction site model self-consistent field explicitly including spatial electron density distribution and successfully applied it to the chemical reactions in aqueous phase.

  17. SYBYL line notation (SLN): a single notation to represent chemical structures, queries, reactions, and virtual libraries.

    PubMed

    Homer, R Webster; Swanson, Jon; Jilek, Robert J; Hurst, Tad; Clark, Robert D

    2008-12-01

    SYBYL line notation (SLN) is a powerful way to represent molecular structures, reactions, libraries of structures, molecular fragments, formulations, molecular queries, and reaction queries. Nearly any chemical structure imaginable, including macromolecules, pharmaceuticals, catalysts, and even combinatorial libraries can be represented as an SLN string. The language provides a rich syntax for database queries comparable to SMARTS. It provides full Markush, R-Group, reaction, and macro atom capabilities in a single unified notation. It includes the ability to specify 3D conformations and 2D depictions. All the information necessary to recreate the structure in a modeling or drawing package is present in a single, concise string of ASCII characters. This makes SLN ideal for structure communication over global computer networks between applications sitting at remote sites. Unlike SMILES and its derivatives, SLN accomplishes this within a single unified syntax. Structures, queries, compounds, reactions, and virtual libraries can all be represented in a single notation. PMID:18998666

  18. Middle atmosphere heating by exothermic chemical reactions involving odd-hydrogen species

    NASA Technical Reports Server (NTRS)

    Mlynczak, Martin G.; Solomon, Susan

    1991-01-01

    The rate of heating which occurs in the middle atmosphere due to four exothermic reactions involving members of the odd-hydrogen family is calculated. The following reactions are considered: O + OH yields O2 + H; H + O2 + M yields HO2 + M; H + O3 yields OH + O2; and O + HO2 yields OH + O2. It is shown that the heating rates due to these reactions rival the oxygen-related heating rates conventionally considered in middle-atmosphere models. The conversion of chemical potential energy into molecular translational energy (heat) by these odd-hydrogen reactions is shown to be a significant energy source in the middle atmosphere that has not been previously considered.

  19. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

    2003-04-01

    The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

  20. CO2 in 1-butyl-3-methylimidazolium acetate. 2. NMR investigation of chemical reactions.

    PubMed

    Besnard, Marcel; Cabao, M Isabel; Vaca Chvez, Fabin; Pinaud, Nol; Sebastio, Pedro J; Coutinho, Joo A P; Mascetti, Jolle; Danten, Yann

    2012-05-24

    The solvation of CO(2) in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been investigated by (1)H, (13)C, and (15)N NMR spectroscopy at low CO(2) molar fraction (mf) (x(CO(2)) ca. 0.27) corresponding to the reactive regime described in part 1 of this study. It is shown that a carboxylation reaction occurs between CO(2) and Bmim Ac, leading to the formation of a non-negligible amount (~16%) of 1-butyl-3-methylimidazolium-2-carboxylate. It is also found that acetic acid molecules are produced during this reaction and tend to form with elapsed time stable cyclic dimers existing in pure acid. A further series of experiments has been dedicated to characterize the influence of water traces on the carboxylation reaction. It is found that water, even at high ratio (0.15 mf), does not hamper the formation of the carboxylate species but lead to the formation of byproduct involving CO(2). The evolution with temperature of the resonance lines associated with the products of the reactions confirms that they have a different origin. The main byproduct has been assigned to bicarbonate. All these results confirm the existence of a reactive regime in the CO(2)-Bmim Ac system but different from that reported in the literature on the formation of a reversible molecular complex possibly accompanied by a minor chemical reaction. Finally, the reactive scheme interpreting the carboxylation reaction and the formation of acetic acid proposed in the literature is discussed. We found that the triggering of the carboxylation reaction is necessarily connected with the introduction of carbon dioxide in the IL. We argue that a more refined scheme is still needed to understand in details the different steps of the chemical reaction in the dense phase. PMID:22533570

  1. Experimental revaluation of the importance of the abstraction channel in the reactions of monoterpenes with OH radicals.

    PubMed

    Rio, Caroline; Flaud, Pierre-Marie; Loison, Jean-Christophe; Villenave, Eric

    2010-12-17

    The primary oxidation steps of (γ-terpinene+OH) and (d-limonene+OH) reactions are investigated using two techniques: an excimer laser photolysis set-up coupled with UV absorption spectrometry performed at atmospheric pressure and a fast-flow reactor coupled to time of flight mass spectrometry at low pressure. OH radicals are generated either by photolysis of H(2)O(2) or via the reaction of H atoms with NO(2). The primary reaction of monoterpenes with hydroxyl radicals can proceed by two reaction pathways: OH-addition and H-abstraction. The branching ratios for these channels are measured at various pressures for (γ-terpinene+OH) and (d-limonene+OH) reactions and a discussion on the H-abstraction importance for reactions of monoterpenes with hydroxyl radicals is proposed. H-abstraction may contribute to (31±9)% and (34±8)% respectively, for γ-terpinene and d-limonene reactions with OH at atmospheric pressure and respectively to (28±6)% and (28±8)% at low pressure (between 0.5 and 2.8 torr). As already pointed out by the Leuven group of Peeters, H-abstraction may be a significant reaction pathway for the reactions of monoterpenes with hydroxyl radicals. Therefore, oxidation products resulting from the H-abstraction should not be neglected in the mechanisms describing the formation of secondary organic aerosols (SOA) from gas-phase reactions of monoterpenes+OH. PMID:21110376

  2. Solar photo-thermal catalytic reactions to produce high value chemicals

    SciTech Connect

    Prengle, H.W. Jr.; Wentworth, W.E.

    1992-04-01

    This report presents a summary of the research work accomplished to date on the utilization of solar photo-thermal energy to convert low cost chemical feedstocks into high $-value chemical products. The rationale is that the solar IR-VIS-UV spectrum is unique, supplying endothermic reaction energy as well as VIS-UV for photochemical activation. Chemical market analysis and product price distribution focused attention on speciality chemicals with prices >$1.00/lb, and a synthesis sequence of n-paraffins to aromatics to partial oxidized products. The experimental work has demonstrated that enhanced reaction effects result from VIS-UV irradiation of catalytically active V2O5/SiO2. Experiments of the past year have been on dehydrogenation and dehydrocyclization of n-paraffins to olefins and aromatics with preference for the latter. Recent results using n-hexane produced 95% conversion with 56% benzene; it is speculated that aromatic yield should reach {approximately}70% by further optimization. Pilot- and commercial-scale reactor configurations have been examined; the odds-on-favorite being a shallow fluid-bed of catalyst with incident radiation from the top. Sequencing for maximum cost effectiveness would be day-time endothermic followed by night-time exothermic reactions to produce the products.

  3. Chemical reactions in a solar furnace by direct solar irradiation of the catalyst

    SciTech Connect

    Levy, M.; Rosin, H.; Levitan, R.

    1989-02-01

    Concentrated solar radiation has been used to heat air in a volumetric receiver device. Such a receiver, using a wire mesh arrangement placed in the focal zone, can also be used for carrying out a chemical reaction where the catalyst is heated directly by the concentrated solar beam without any intermediary heat transfer fluid. The advantage of such a concept is that the highest temperature of the whole system is at the reaction site and not on the wall of the reactor or in the heat transfer fluid. Thus, higher conversion efficiencies will be obtained. Moreover, as the reaction site is directly irradiated by a very intense solar flux, photochemically enhanced reactions may result under certain conditions. The disadvantage of the approach is the difficulty in insuring uniform insolation and temperature distribution throughout the catalyst surface. Another problem is that a transparent window is required to seal off the reactants from the environment; this may complicate scaling up of the process. In this communication the authors report the results of preliminary experiments demonstrating that catalysed chemical reactions can be carried out by direct solar irradiation of the catalyst.

  4. Spatially orthogonal chemical functionalization ofa hierarchical pore network for catalytic cascadereactions.

    PubMed

    Parlett, Christopher M A; Isaacs, Mark A; Beaumont, Simon K; Bingham, Laura M; Hondow, Nicole S; Wilson, Karen; Lee, Adam F

    2016-02-01

    The chemical functionality within porous architectures dictates their performance as heterogeneous catalysts; however, synthetic routes to control the spatial distribution of individual functions within porous solids are limited. Here we report the fabrication of spatially orthogonal bifunctional porous catalysts, through the stepwise template removal and chemical functionalization of an interconnected silica framework. Selective removal of polystyrene nanosphere templates from a lyotropic liquid crystal-templated silica sol-gel matrix, followed by extraction of the liquid crystal template, affords a hierarchical macroporous-mesoporous architecture. Decoupling of the individual template extractions allows independent functionalization of macropore and mesopore networks on the basis of chemical and/or size specificity. Spatial compartmentalization of, and directed molecular transport between, chemical functionalities affords control over the reaction sequence in catalytic cascades; herein illustrated by the Pd/Pt-catalysed oxidation of cinnamyl alcohol to cinnamic acid. We anticipate that our methodology will prompt further design of multifunctional materials comprising spatially compartmentalized functions. PMID:26569475

  5. Spatially orthogonal chemical functionalization of a hierarchical pore network for catalytic cascade reactions

    NASA Astrophysics Data System (ADS)

    Parlett, Christopher M. A.; Isaacs, Mark A.; Beaumont, Simon K.; Bingham, Laura M.; Hondow, Nicole S.; Wilson, Karen; Lee, Adam F.

    2016-02-01

    The chemical functionality within porous architectures dictates their performance as heterogeneous catalysts; however, synthetic routes to control the spatial distribution of individual functions within porous solids are limited. Here we report the fabrication of spatially orthogonal bifunctional porous catalysts, through the stepwise template removal and chemical functionalization of an interconnected silica framework. Selective removal of polystyrene nanosphere templates from a lyotropic liquid crystal-templated silica sol-gel matrix, followed by extraction of the liquid crystal template, affords a hierarchical macroporous-mesoporous architecture. Decoupling of the individual template extractions allows independent functionalization of macropore and mesopore networks on the basis of chemical and/or size specificity. Spatial compartmentalization of, and directed molecular transport between, chemical functionalities affords control over the reaction sequence in catalytic cascades; herein illustrated by the Pd/Pt-catalysed oxidation of cinnamyl alcohol to cinnamic acid. We anticipate that our methodology will prompt further design of multifunctional materials comprising spatially compartmentalized functions.

  6. Importance of polarization transfer in reaction products for interpreting and analyzing CIDNP at low magnetic fields

    NASA Astrophysics Data System (ADS)

    Pravdivtsev, Andrey N.; Yurkovskaya, Alexandra V.; Ivanov, Konstantin L.; Vieth, Hans-Martin

    2015-05-01

    The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) was studied for the amino acids N-acetyl histidine, N-acetyl tryptophan and N-acetyl tyrosine. It is demonstrated that at low field CIDNP is strongly affected by polarization redistribution in the diamagnetic molecules. Such a polarization transfer is of coherent nature and is due to spin coherences formed together with non-equilibrium population of the spin states. These coherences clearly manifest themselves in an oscillatory time dependence of polarization. Polarization transfer effects are most pronounced at nuclear spin Level Anti-Crossings (LACs), which also result in sharp features in the CIDNP field dependence. Thus, polarization transfer is an important factor, which has to be taken into account in order to interpret low-field CIDNP data on both qualitative and quantitative level. Possible applications of polarization transfer phenomena are also discussed in the paper. In particular, the role of LACs in spin order transfer is highlighted: LACs provide a new tool for precise manipulation of spin hyperpolarization and NMR enhancement of selected target spins.

  7. Chemical TOPAZ: Modifications to the heat transfer code TOPAZ: The addition of chemical reaction kinetics and chemical mixtures

    SciTech Connect

    Nichols, A.L. III.

    1990-06-07

    This is a report describing the modifications which have been made to the heat flow code TOPAZ to allow the inclusion of thermally controlled chemical kinetics. This report is broken into parts. The first part is an introduction to the general assumptions and theoretical underpinning that were used to develop the model. The second section describes the changes that have been implemented into the code. The third section is the users manual for the input for the code. The fourth section is a compilation of hints, common errors, and things to be aware of while you are getting started. The fifth section gives a sample problem using the new code. This manual addenda is written with the presumption that most readers are not fluent with chemical concepts. Therefore, we shall in this section endeavor to describe the requirements that must be met before chemistry can occur and how we have modeled the chemistry in the code.

  8. Mechanism of a chemical classic: quantum chemical investigation of the autocatalyzed reaction of the serendipitous whler synthesis of urea.

    PubMed

    Tsipis, Constantinos A; Karipidis, Paraskevas A

    2003-02-26

    The detailed reaction pathways for the ammonium cyanate transformation into urea (Whler's reaction) in the gas phase, in solution, and in the solid state have exhaustively been explored by means of first-principles quantum chemical calculations at the B3LYP level of theory using the 6-31G(d,p) basis set. This serendipitous synthesis of urea is predicted to proceed in two steps; the first step involves the decomposition of the ammonium cyanate to ammonia and isocyanic or cyanic acid, and the second one, which is the main reaction step (and probably the rate-determining step), involves the interaction of NH(3) with either isocyanic or cyanic acid. Several alternative pathways were envisaged for the main reaction step of Whler's reaction in a vacuum involving the formation of "four-center" transition states. Modeling Whler's reaction in aqueous solution and in the solid state, it was found that the addition of NH(3) to both acids is assisted (autocatalyzed) by the active participation of extra H(2)O and/or NH(3) molecules, through a preassociative, cooperative, and hydrogen-transfer relay mechanism involving the formation of "six-center" or even "eight-center" transition states. The most energetically economic path of the rate-determining step of Whler's reaction is that of the addition of NH(3) to the C=N double bond of isocyanic acid, directly affording urea. An alternative pathway corresponding to the anti-addition of ammonia to the Ctbd1;N triple bond of cyanic acid, yielding urea's tautomer HN=C(OH)NH(2), seems to be another possibility. In the last case, urea is formed through a prototropic tautomerization of its enolic form. The energies of the reactants, products, and all intermediates along with the barrier heights for each reaction path have been calculated at the B3LYP/6-31G(d,p) level of theory. The geometry optimization and characterization of all of the stationary points found on the potential energy hypersurfaces was performed at the same level of theory. PMID:12590561

  9. Influence of Alumina Reaction Tube Impurities on the Oxidation of Chemically-Vapor-Deposited Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth

    1995-01-01

    Pure coupons of chemically vapor deposited (CVD) SiC were oxidized for 100 h in dry flowing oxygen at 1300 C. The oxidation kinetics were monitored using thermogravimetry (TGA). The experiments were first performed using high-purity alumina reaction tubes. The experiments were then repeated using fused quartz reaction tubes. Differences in oxidation kinetics, scale composition, and scale morphology were observed. These differences were attributed to impurities in the alumina tubes. Investigators interested in high-temperature oxidation of silica formers should be aware that high-purity alumina can have significant effects on experiment results.

  10. Parity conservation and polarization of differential cross sections in complex-forming chemical reactions.

    PubMed

    Bonnet, L; Larrgaray, P; Rayez, J-C; Gonzalez-Lezana, T

    2006-09-14

    For complex-forming chemical reactions, such as atom-diatom insertion reactions, quantum scattering and quantum statistical calculations usually predict sharp forward/backward peaks in the Differential Cross Sections (DCS). Conversely, the corresponding classical calculations are unable to reproduce these peaks. We show here that the basic reason for such an intriguing failure is that parity conservation is ignored in classical mechanics. A by-product of the analysis is a simple parity-restoring approximation that might significantly increase the ability of classical mechanics to describe DCSs over the whole angular range for the title processes. PMID:17028685

  11. Simulations of isoprene: Ozone reactions for a general circulation/chemical transport model

    NASA Technical Reports Server (NTRS)

    Makar, P. A.; Mcconnell, J. C.

    1994-01-01

    A parameterized reaction mechanism has been created to examine the interactions between isoprene and other tropospheric gas-phase chemicals. Tests of the parameterization have shown that its results match those of a more complex reaction set to a high degree of accuracy. Comparisons between test runs have shown that the presence of isoprene at the start of a six day interval can enhance later ozone concentrations by as much as twenty-nine percent. The test cases used no input fluxes beyond the initial time, implying that a single input of a biogenic hydrocarbon to an airmass can alter its ozone chemistry over a time scale on the order of a week.

  12. Metal Oxide Nanoparticles: The Importance of Size, Shape, Chemical Composition, and Valence State in Determining Toxicity

    NASA Astrophysics Data System (ADS)

    Dunnick, Katherine

    Nanoparticles, which are defined as a structure with at least one dimension between 1 and 100 nm, have the potential to be used in a variety of consumer products due to their improved functionality compared to similar particles of larger size. Their small size is associated with increased strength, improved catalytic properties, and increased reactivity; however, their size is also associated with increased toxicity in vitro and in vivo. Numerous toxicological studies have been conducted to determine the properties of nanomaterials that increase their toxicity in order to manufacture new nanomaterials with decreased toxicity. Data indicates that size, shape, chemical composition, and valence state of nanomaterials can dramatically alter their toxicity profile. Therefore, the purpose of this dissertation was to determine how altering the shape, size, and chemical composition of various metal oxide nanoparticles would affect their toxicity. Metal oxides are used in variety of consumer products, from spray-sun screens, to food coloring agents; thus, understanding the toxicity of metal oxides and determining which aspects affect their toxicity may provide safe alternatives nanomaterials for continued use in manufacturing. Tungstate nanoparticles toxicity was assessed in an in vitro model using RAW 264.7 cells. The size, shape, and chemical composition of these nanomaterials were altered and the effect on reactive oxygen species and general cytotoxicity was determined using a variety of techniques. Results demonstrate that shape was important in reactive oxygen species production as wires were able to induce significant reactive oxygen species compared to spheres. Shape, size, and chemical composition did not have much effect on the overall toxicity of these nanoparticles in RAW 264.7 cells over a 72 hour time course, implicating that the base material of the nanoparticles was not toxic in these cells. To further assess how chemical composition can affect toxicity, cerium oxide nanoparticles were chemically modified using a process known as doping, to alter their valence state. The size and shape of the cerium oxide nanoparticles remained constant. Overall, results indicated that cerium oxide was not toxic in both RLE-6TN and NR8383 pulmonary rat cells, however, chemically modifying the valence state of the nanomaterial did affect the antioxidant potential. To determine if this trend was measureable in vivo, rats were exposed to various cerium oxide nanoparticles via intratracheal instillation and damage, changes in pulmonary cell differentials, and phagocytic cell activity were assessed. Results implicate that chemically modifying the nanoparticles had an effect on the overall damage induced by the material but did not dramatically affect inflammatory potential or phagocytic cell activity. Overall the data from these studies imply that size, shape, chemical composition, and valence state of nanomaterials can be manipulated to alter their toxicity.

  13. Ab initio studies of equations of state and chemical reactions of reactive structural materials

    NASA Astrophysics Data System (ADS)

    Zaharieva, Roussislava

    The motivations for the research issues addressed in this thesis are based on the needs of the aerospace structural analysis and the design community. The specific focus is related to the characterization and shock induced chemical reactions of multi-functional structural-energetic materials that are also known as the reactive structural materials and their reaction capabilities. Usually motivation for selection of aerospace structural materials is to realize required strength characteristics and favorable strength to weight ratios. The term strength implies resistance to loads experienced during the service life of the structure, including resistance to fatigue loads, corrosion and other extreme conditions. Thus, basically the structural materials are single function materials that resist loads experienced during the service life of the structure. However, it is desirable to select materials that are capable of offering more than one basic function of strength. Very often, the second function is the capability to provide functions of sensing and actuation. In this thesis, the second function is different. The second function is the energetic characteristics. Thus, the choice of dual functions of the material are the structural characteristics and energetic characteristics. These materials are also known by other names such as the reactive material structures or dual functional structural energetic materials. Specifically the selected reactive materials include mixtures of selected metals and metal oxides that are also known as thermite mixtures, reacting intermetallic combinations and oxidizing materials. There are several techniques that are available to synthesize these structural energetic materials or reactive material structures and new synthesis techniques constitute an open research area. The focus of this thesis, however, is the characterization of chemical reactions of reactive material structures that involve two or more solids (or condensed matter). The subject of studies of the shock or thermally induced chemical reactions of the two solids comprising these reactive materials, from first principles, is a relatively new field of study. The published literature on ab initio techniques or quantum mechanics based approaches consists of the ab initio or ab initio-molecular dynamics studies in related fields that contain a solid and a gas. One such study in the literature involves a gas and a solid. This is an investigation of the adsorption of gasses such as carbon monoxide (CO) on Tungsten. The motivation for these studies is to synthesize alternate or synthetic fuel technology by Fischer-Tropsch process. In this thesis these studies are first to establish the procedure for solid-solid reaction and then to extend that to consider the effects of mechanical strain and temperature on the binding energy and chemisorptions of CO on tungsten. Then in this thesis, similar studies are also conducted on the effect of mechanical strain and temperature on the binding energies of Titanium and hydrogen. The motivations are again to understand the method and extend the method to such solid-solid reactions. A second motivation is to seek strained conditions that favor hydrogen storage and strain conditions that release hydrogen easily when needed. Following the establishment of ab initio and ab initio studies of chemical reactions between a solid and a gas, the next step of research is to study thermally induced chemical reaction between two solids (Ni+Al). Thus, specific new studies of the thesis are as follows: (1) Ab initio Studies of Binding energies associated with chemisorption of (a) CO on W surfaces (111, and 100) at elevated temperatures and strains and (b) adsorption of hydrogen in titanium base. (2) Equations of state of mixtures of reactive material structures from ab initio methods. (3) Ab initio studies of the reaction initiation, transition states and reaction products of intermetallic mixtures of (Ni+Al) at elevated temperatures and strains. (4) Press-cure synthesis of Nano-nickel and nano-aluminum based reactive material structures and DTA tests to study experimentally initiation of chemical reactions, due to thermal energy input.

  14. SCRIPDB: a portal for easy access to syntheses, chemicals and reactions in patents

    PubMed Central

    Heifets, Abraham; Jurisica, Igor

    2012-01-01

    The patent literature is a rich catalog of biologically relevant chemicals; many public and commercial molecular databases contain the structures disclosed in patent claims. However, patents are an equally rich source of metadata about bioactive molecules, including mechanism of action, disease class, homologous experimental series, structural alternatives, or the synthetic pathways used to produce molecules of interest. Unfortunately, this metadata is discarded when chemical structures are deposited separately in databases. SCRIPDB is a chemical structure database designed to make this metadata accessible. SCRIPDB provides the full original patent text, reactions and relationships described within any individual patent, in addition to the molecular files common to structural databases. We discuss how such information is valuable in medical text mining, chemical image analysis, reaction extraction and in silico pharmaceutical lead optimization. SCRIPDB may be searched by exact chemical structure, substructure or molecular similarity and the results may be restricted to patents describing synthetic routes. SCRIPDB is available at http://dcv.uhnres.utoronto.ca/SCRIPDB. PMID:22067445

  15. A Method for Incorporating Chemical Reactions into Multiphase Flow Models for CO2 Injection

    NASA Astrophysics Data System (ADS)

    Saaltink, M. W.; Vilarrasa, V.; De Gaspari, F.; Silva, O.; Carrera, J.

    2012-04-01

    CO2 injection in deep saline aquifers involves many different processes, including multiphase flow, heat and mass transport, rock deformation and minerals precipitation and dissolution. All these processes are coupled. Therefore, their modeling is difficult and requires complex computer codes to describe and assess them numerically. We developed a method for incorporating chemical reactions into multiphase flow codes. It is limited to chemical systems that can be calculated as a function of the state variables of the multiphase flow model (e.g. liquid pressure, gas pressure, temperature). It consists of calculating the chemical composition of this system as a function of these state variables by means of chemical speciation codes and redefining the components of the multiphase flow code (e.g., water, CO2). We applied this method to incorporate chemical reactions of a H2O-CO2-NaCl-CaCO3 system into CodeBright, a code that can handle multiphase flow, heat transport, mass transport and deformation. We used this code to model CO2 injection into a saline aquifer containing calcite. The model could simulate well the interaction between the development of the CO2 bubble, dissolution of CO2 into the brine, calcite dissolution and density dependent flow.

  16. Plasmonic Properties of Bimetallic Nanostructures and Their Applications in Hydrogen Sensing and Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Jiang, Ruibin

    Noble metal nanocrystals have attracted great interest from a wide range of research fields because of their intriguing properties endowed by their localized surface plasmon resonances, which are the collective oscillations of free electrons. Under resonant excitation, metal nanostructures exhibit very large scattering and absorption cross sections and large near-field enhancement. These extraordinary properties can be used in different applications, such as plasmonic sensing and imaging, plasmon-controlled optics, photothermal therapy, photocatalysis, solar cells, and so on. Gold and Silver nanocrystals have plasmon resonances in the visible and near-infrared regions. However, gold and silver are not suitable for some applications. For example, they are generally inactive for catalyzing chemical reactions. The integration of plasmonic metals with other metals can offer superior or new physical/chemical properties. In this thesis, I prepared Au/Ag and Au/Pd bimetallic nanostructures and studied their plasmonic properties and applications in hydrogen sensing and photocatalysis. Seeds have a crucial importance in the synthesis of bimetallic nanostructures. I therefore first studied the roles of the crystalline structure and shape of seeds on the overgrowth of bimetallic nanostructures. The overgrowth of silver and palladium on single crystalline Au nanorods, multicrystalline Au nanorods, and nanobipyramids were studied under the same conditions for each metal. The growths of silver and palladium on single crystalline Au nanorods gave cuboidal nanostructures, while rod-shaped nanostructures were obtained from the growths of silver and palladium on multicrystalline Au nanorods and nanobipyramids. Moreover, the growths of silver and palladium on multicrystalline Au nanobipyramids started at the stepped side facets, while the growths started at the twin boundaries on multicrystalline Au nanorods. These results unambiguously indicate that the crystalline structure of seeds plays a significant role on the final morphologies of multimetallic nanostructures, while the seed shape has a prominent effect on the growth kinetics. Four plasmon resonance bands were observed in Au/Ag bimetallic nanocrystals. I then studied the evolution and nature of the four plasmon bands during the silver coating on Au nanorods both experimentally and theoretically. Electrodynamic simulations revealed that the lowest-energy peak belongs to the longitudinal dipolar plasmon mode, the second-lowest-energy peak is the transverse dipolar plasmon mode, and the two highest-energy peaks can be attributed to octupolar plasmon modes. The retardation effect and the interference between two perpendicularly polarized excitations along the edge directions are important for the formation of the distinct highest-energy and second-highest-energy octupolar plasmon modes, respectively. As the Ag shell thickness is increased, the longitudinal plasmon mode blue-shifts, the transverse plasmon mode first blue-shifts and then red-shifts slightly, and the two octupolar plasmon modes stay at nearly constant wavelengths. The extinction intensities of all the four plasmon bands increase with the increase of the overall particle size. Palladium is widely used in hydrogen sensing and catalysis. I therefore studied the applications of Au/Pd bimetallic nanostructures in hydrogen sensing and photocatalysis. Two types of Au/Pd bimetallic nanostructures, nanostructures with continuous and discontinuous Pd shells, were employed to study their hydrogen sensing performances. For the nanostructures with continuous Pd shell, the hydrogen sensing performances were improved with the increase in the Pd shell thickness. A plasmon shift of 56 nm was observed when the hydrogen concentration was 4%. The nanostructures with discontinuous Pd shell exhibited smaller plasmon shifts compared with those with continuous Pd shell. For the photocatalytic application of Au/Pd bimetallic nanostructures, I studied their photocatalytic performance for Suzuki coupling reactions. The results indicate that plasmonic Au/Pd bimetallic nanostructures can efficiently harvest light energy for chemical reactions. The intimate integration of plasmonic and catalytic components in one nanostructure enables the light energy absorbed by the plasmonic component to be directly transferred to the catalytic component. Both hot electron transfer and photothermal heating contribute to the plasmon-enhanced chemical reactions. The photothermal effect is a nonlocal heating and the contribution of the hot electron transfer effect is dependent on the environmental temperature. Therefore, the photothermal heating effect can promote the hot electron transfer effect. I believe that my research work will be very helpful for the design and application of plasmonic bimetallic nanostructures. My study on the plasmonic properties of Au/Ag bimetallic nanocrystals has deepened the understanding of the plasmons of Au/Ag nanorods and will be helpful for utilizing the different modes to achieve specific functions. The hydrogen sensing and photocatalysis of Au/Pd bimetallic nanostructures have shown that the integration of functional components with plasmonic nanostructures can achieve unconventional properties, which will flourish the applications of plasmons in life sciences, energy, and environmental areas.

  17. Numerical simulation of the interaction of transport, diffusion and chemical reactions in an urban plume

    NASA Technical Reports Server (NTRS)

    Vogel, Bernhard; Vogel, Heike; Fiedler, Franz

    1994-01-01

    A model system is presented that takes into account the main physical and chemical processes on the regional scale here in an area of 100x100 sq km. The horizontal gridsize used is 2x2 sq km. For a case study, it is demonstrated how the model system can be used to separate the contributions of the processes advection, turbulent diffusion, and chemical reactions to the diurnal cycle of ozone. In this way, typical features which are visible in observations and are reproduced by the numerical simulations can be interpreted.

  18. Investigation of shock-induced and shock-assisted chemical reactions in molybdenum-silicon powder mixtures

    NASA Astrophysics Data System (ADS)

    Vandersall, Kevin Stewart

    1999-10-01

    In this research, chemical reactions occurring in molybdenum and silicon powder mixtures under "shock-induced" (those occurring during the high-pressure shock state) and "shock-assisted" (those occurring subsequent to the shock event, but due to bulk temperature increases) conditions were investigated. Differences in the densities and yield strengths of the two constituents, in addition to the large heat of reaction associated with molybdenum disilicide (MoSi2) formation can lead to shock-induced as well as shock-assisted reactions, which make this an ideal system to delineate the kinetics and mechanisms of reactions occurring in shock-compressed powder mixtures. Shock recovery experiments performed on Mo + 2 Si powder mixtures employing cylindrical implosion geometry showed thermally initiated reactions. A mixed phase eutectic type microstructure of MoSi2 and Mo 5Si3, resulting from reaction occurring due to melting of both reactants, was observed in axial regions of the cylindrical compacts. In regions surrounding the mach stem, melting of only silicon and reaction occurring via dissolution and re-precipitation forming MoSi2 spherules surrounding molybdenum particles in a melted and solidified silicon matrix was observed. The planar pressure shock recovery geometry showed a single phase MoSi2, microstructure formed due to a solid-state pressure-induced reaction process. The time-resolved instrumented experiments were performed using a single stage gas gun in the velocity range of 500 m/s to 1 km/s, and employed poly-vinyl di-flouride (PVDF) stress gauges placed at the front and rear surfaces of the powder to determine the crush strength, densification history, and reaction initiation threshold conditions. Time-resolved experiments performed on 58% dense Mo + 2 Si powder mixtures at input stresses less than 4 GPa, showed characteristics of powder densification and dispersed propagated wave stress profiles with rise time >40 nanoseconds. At input stress between 4--6 GPa, the powder mixtures showed a sharp rise time (<10 ns) of propagated wave profile and an expanded state of products revealing conclusive evidence of shock-induced reaction. At input stresses greater than 6 GPa, the powder mixtures showed a lower rise time and transition to a low-compressibility (melt) state indicating lack of shock-induced reaction. The results of this work show that (a) premature formation of a melt phase restricts mixing between reactants and inhibits "shock-induced" reaction initiation, although "shock-assisted" reactions can still occur in time scales of thermal equilibrium, and (b) the crush strength of powder mixtures is the most important parameter that controls initiation of a "shock-induced" reaction. Reaction synthesis experiments conducted on 55--95% dense Mo + 2 Si powder mixture compacts under an applied electric field showed that SHS reactions that would have normally become extinguished without the application of electric field, were observed to be self-sustained. Under such conditions, the reaction kinetics were observed to be enhanced and the reaction products showed a highly refined microstructure.

  19. Monitoring the inorganic chemical reaction by surface-enhanced Raman spectroscopy: A case of Fe(3+) to Fe(2+) conversion.

    PubMed

    Qin, Suhua; Meng, Juan; Tang, Xianghu; Yang, Liangbao

    2016-01-01

    Monitoring the process of organic chemical reactions to study the kinetics by surface-enhanced Raman spectroscopy (SERS) is currently of immense interest. However, monitoring the inorganic chemical reaction is still an extremely difficulty for researchers. This study exactly focused on the monitor of inorganic chemical reaction. Capillary coated with silver nanoparticles was introduced, which was an efficient platform for monitoring reactions with SERS due to the advantages of sensitivity and excellent reproducibility. The photoreduction of [Fe(phen)3](3+) to [Fe(phen)3](2+) was used as model reaction to demonstrated the feasibility of SERS monitoring inorganic chemical reaction by involving in metal-organic complexes. Moreover, the preliminary implementation demonstrated that the kinetics of photoreduction can be real-time monitored by in situ using the SERS technique on a single constructed capillary, which may be useful for the practical application of SERS technique. PMID:26695289

  20. Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

    Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

  1. Gas chromatography plasma-assisted reaction chemical ionization mass spectrometry for quantitative detection of bromine in organic compounds.

    PubMed

    Lin, Ninghang; Wang, Haopeng; Kahen, Kaveh; Badiei, Hamid; Jorabchi, Kaveh

    2014-08-01

    We have recently introduced plasma-assisted reaction chemical ionization mass spectrometry (PARCI-MS) for elemental analysis of halogens in organic compounds. Here, we utilize gas chromatography (GC) coupled to PARCI-MS to investigate the mechanism of Br(-) ion generation from organobromines and to evaluate analytical performance of PARCI for organobromine analysis. Bromine atoms in compounds eluting from GC are converted to HBr in a low-pressure microwave induced helium plasma with trace amounts of hydrogen added as a reaction gas. Ionization is achieved by introducing nitrogen into the afterglow region of the plasma, liberating electrons via penning ionization and leading to formation of negative ions. We demonstrate that N2 largely affects the ionization process, whereas H2 affects both the ionization process and in-plasma reactions. Our investigations also suggest that dissociative electron capture is the main ionization route for formation of Br(-) ions. Importantly, GC-PARCI-MS shows a uniform response factor for bromine across brominated compounds of drastically different chemical structures, confirming PARCI's ability to quantify organobromines in the absence of compound-specific standards. Over 3 orders of magnitude linear dynamic range is demonstrated for bromine quantification. We report a detection limit of 29 fg of bromine on-column, ~4-fold better than inductively coupled plasma-MS. PMID:25003497

  2. Chemical reaction mechanisms in solution from brute force computational Arrhenius plots

    PubMed Central

    Kazemi, Masoud; qvist, Johan

    2015-01-01

    Decomposition of activation free energies of chemical reactions, into enthalpic and entropic components, can provide invaluable signatures of mechanistic pathways both in solution and in enzymes. Owing to the large number of degrees of freedom involved in such condensed-phase reactions, the extensive configurational sampling needed for reliable entropy estimates is still beyond the scope of quantum chemical calculations. Here we show, for the hydrolytic deamination of cytidine and dihydrocytidine in water, how direct computer simulations of the temperature dependence of free energy profiles can be used to extract very accurate thermodynamic activation parameters. The simulations are based on empirical valence bond models, and we demonstrate that the energetics obtained is insensitive to whether these are calibrated by quantum mechanical calculations or experimental data. The thermodynamic activation parameters are in remarkable agreement with experiment results and allow discrimination among alternative mechanisms, as well as rationalization of their different activation enthalpies and entropies. PMID:26028237

  3. Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation.

    PubMed

    Ibrahim, Heide; Wales, Benji; Beaulieu, Samuel; Schmidt, Bruno E; Thir, Nicolas; Fowe, Emmanuel P; Bisson, ric; Hebeisen, Christoph T; Wanie, Vincent; Gigure, Mathieu; Kieffer, Jean-Claude; Spanner, Michael; Bandrauk, Andr D; Sanderson, Joseph; Schuurman, Michael S; Lgar, Franois

    2014-01-01

    The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging, we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using vacuum ultraviolet light from a free-electron laser. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and quantitative ab initio trajectory simulations. PMID:25034613

  4. Interaction of 2-aminopyrimidine with ?- and ?-acceptors involving chemical reactions via initial charge transfer complexation

    NASA Astrophysics Data System (ADS)

    Rabie, U. M.; Abou-El-Wafa, M. H.; Mohamed, R. A.

    2007-12-01

    Interaction of 2-aminopyrimidine (AP) with iodine as a typical ?-type acceptor and with a typical ?-type acceptor, 2,3,5,6-tetrachloro-1,4-benzoquinone, p-chloranil (CHL) have been studied spectrophotometrically. Electronic absorption spectra of the system AP-I 2 in several organic solvents of different polarities have performed clear charge transfer (CT) band(s). Formation constants ( KCT) and molar absorption coefficients ( ?CT) and thermodynamic properties, ? H, ? S, and ? G, of this system in various organic solvents were determined and discussed. Interaction of AP with the ?-acceptor has shown unique behaviors. Chemical reaction has occurred via prior or initial formation of the outer-sphere CT complex followed by formation of the corresponding anion radicals, CHL rad - , as intermediates. UV-vis, 1H NMR, Mass, and FT-IR spectra in addition to the elemental analysis were used to confirm the proposed occurrence of the chemical reaction and to investigate the synthesized solid products.

  5. Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation

    NASA Astrophysics Data System (ADS)

    Ibrahim, Heide; Wales, Benji; Beaulieu, Samuel; Schmidt, Bruno E.; Thir, Nicolas; Fowe, Emmanuel P.; Bisson, ric; Hebeisen, Christoph T.; Wanie, Vincent; Gigure, Mathieu; Kieffer, Jean-Claude; Spanner, Michael; Bandrauk, Andr D.; Sanderson, Joseph; Schuurman, Michael S.; Lgar, Franois

    2014-07-01

    The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging, we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using vacuum ultraviolet light from a free-electron laser. Here we show that 266?nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and quantitative ab initio trajectory simulations.

  6. Graphene-Semiconductor Catalytic Nanodiodes for Quantitative Detection of Hot Electrons Induced by a Chemical Reaction.

    PubMed

    Lee, Hyosun; Nedrygailov, Ievgen I; Lee, Young Keun; Lee, Changhwan; Choi, Hongkyw; Choi, Jin Sik; Choi, Choon-Gi; Park, Jeong Young

    2016-03-01

    Direct detection of hot electrons generated by exothermic surface reactions on nanocatalysts is an effective strategy to obtain insight into electronic excitation during chemical reactions. For this purpose, we fabricated a novel catalytic nanodiode based on a Schottky junction between a single layer of graphene and an n-type TiO2 layer that enables the detection of hot electron flows produced by hydrogen oxidation on Pt nanoparticles. By making a comparative analysis of data obtained from measuring the hot electron current (chemicurrent) and turnover frequency, we demonstrate that graphene's unique electronic structure and extraordinary material properties, including its atomically thin nature and ballistic electron transport, allow improved conductivity at the interface between the catalytic Pt nanoparticles and the support. Thereby, graphene-based nanodiodes offer an effective and facile way to approach the study of chemical energy conversion mechanisms in composite catalysts with carbon-based supports. PMID:26910271

  7. [Significance of morphofunctional assessment of tissue basophil reactions in prognostication of harmful effects of chemical substances].

    PubMed

    Iaglov, V V; Sheina, N I; Fesenko, M A

    1991-01-01

    The article contains a comparative analysis of experimental data on the assessment of the general toxicological, gonadotrophic effects and morphofunctional reactions of tissue basophils under the influence of 4-bromine-o-xylene, carbon disulfide and pyracryl. Established was the gonadotrophic action of pyracryl against the growing activity of tissue basophils manifested through increased infiltration and high-level degranulation in female rats' reproductive organs. Demonstrated was that, under the influence of low-intensity chemical factors, tissue basophils morphofunctional reactions were those of organ-related nature. The quantitative assessment of tissue basophils was proposed as an informative model for studies of selective (gonadotrophic) actions of low-intensity chemical substances. PMID:1869080

  8. Chemical reaction at ferromagnet/oxide interface and its influence on anomalous Hall effect

    SciTech Connect

    Liu, Yi-Wei; Teng, Jiao E-mail: ghyu@mater.ustb.edu.cn; Zhang, Jing-Yan; Liu, Yang; Chen, Xi; Li, Xu-Jing; Feng, Chun; Wang, Hai-Cheng; Li, Ming-Hua; Yu, Guang-Hua E-mail: ghyu@mater.ustb.edu.cn; Wu, Zheng-Long

    2014-09-08

    Chemical reactions at the ferromagnet/oxide interface in [Pt/Fe]{sub 3}/MgO and [Pt/Fe]{sub 3}/SiO{sub 2} multilayers before and after annealing were investigated by X-ray photoelectron spectroscopy. The results show that Fe atoms at the Fe/MgO interface were completely oxidized in the as-grown state and significantly deoxidized after vacuum annealing. However, only some of the Fe atoms at the Fe/SiO{sub 2} interface were oxidized and rarely deoxidized after annealing. The anomalous Hall effect was modified by this interfacial chemical reaction. The saturation anomalous Hall resistance (R{sub xy}) was greatly increased in the [Pt/Fe]{sub 3}/MgO multilayers after annealing and was 350% higher than that in the as-deposited film, while R{sub xy} of the [Pt/Fe]{sub 3}/SiO{sub 2} multilayer only increased 10% after annealing.

  9. Simultaneous Chemical and Optical Patterning of Polyacrylonitrile Film by Vapor-Based Reaction.

    PubMed

    Shin, Jae-Won; Lee, Choonghyeon; Cha, Sang-Ho; Jang, Jyongsik; Lee, Kyung Jin

    2015-06-01

    The surface of polyacrylonitrile (PAN) film is treated with ethyleneamines (EDA) in a simple chemical vapor phase reaction. Successful introduction of amine functional groups on the cyano group of PAN backbone is verified by FT-IR and NMR measurements. Further UV-vis and photoluminescence analyses show a red shift of the emission peak after repeated EDA treatment, which might be attributed to the formation of imine conjugation from newly formed carbon-nitrogen bonds on the PAN backbone. Further confocal laser scanning microscopy reveals that selective patterning of EDA on PAN films is possible via local polydimethylsiloxane masking. The results indicate that both chemical and optical patterning on PAN film can be realized via a single reaction and show the potential of this novel methodology in selective patterning. PMID:25855336

  10. Amplification of Pressure Waves during Vibrational Equilibration of Excited Chemical Reaction Products

    SciTech Connect

    Tarver, C M

    2004-05-11

    The Non-Equilibrium Zeldovich - von Neumann - Doring (NEZND) theory of self-sustaining detonation identified amplification of pressure wavelets during equilibration of vibrationally excited reaction products in the reaction zone as the physical mechanism by which exothermic chemical energy release sustains detonation waves. This mechanism leads to the formation of the well-known, complex three-dimensional structure of a self-sustaining detonation wave. This amplification mechanism is postulated to be a general property of subsonic and supersonic reactive flows occurring during: shock to detonation transition (SDT); hot spot ignition and growth; deflagration to detonation transition (DDT); flame acceleration by shock or compression waves; and acoustic (sound) wave amplification. The existing experimental and theoretical evidence for pressure wave amplification by chemical energy release into highly vibrationally excited product molecules under these reactive flow conditions is reviewed in this paper.

  11. Deprotection reaction kinetics in chemically amplified photoresists determined by sub-millisecond post exposure bake

    NASA Astrophysics Data System (ADS)

    Jung, Byungki; Ober, Christopher K.; Thompson, Michael O.

    2012-03-01

    Chemically amplified photoresists require a post exposure bake (PEB) to induce deprotection using a UV generated acid-catalyst. While reaction pathways for deprotection have been proposed, key challenges remain in modeling the reaction kinetics. In this work, we used a scanning line-focused laser beam as an alternate PEB method, to quantify the deprotection reaction kinetics of an ESCAP-type and a 193 nm model resist system at high temperatures in millisecond time frames. Results were compared with conventional PEB at 115C for seconds time frames. Results show that the deprotection kinetics follow simple first-order reaction models only under laser PEB conditions, with more complex kinetics observed under hot plate PEB. FT-IR and NMR spectroscopies were used to characterize the reaction byproducts. Results suggest potential differences in deprotection mechanisms between the two PEB temperature and time regimes. The deprotection behavior obtained using this l-PEB technique enables a deeper understanding of the reaction kinetics of photoresists, critical for current DUV and future EUV technologies.

  12. A Microscale Approach to Chemical Kinetics in the General Chemistry Laboratory: The Potassium Iodide Hydrogen Peroxide Iodine-Clock Reaction

    ERIC Educational Resources Information Center

    Sattsangi, Prem D.

    2011-01-01

    A microscale laboratory for teaching chemical kinetics utilizing the iodine clock reaction is described. Plastic pipets, 3 mL volume, are used to store and deliver precise drops of reagents and the reaction is run in a 24 well plastic tray using a total 60 drops of reagents. With this procedure, students determine the rate of reaction and the…

  13. A Microscale Approach to Chemical Kinetics in the General Chemistry Laboratory: The Potassium Iodide Hydrogen Peroxide Iodine-Clock Reaction

    ERIC Educational Resources Information Center

    Sattsangi, Prem D.

    2011-01-01

    A microscale laboratory for teaching chemical kinetics utilizing the iodine clock reaction is described. Plastic pipets, 3 mL volume, are used to store and deliver precise drops of reagents and the reaction is run in a 24 well plastic tray using a total 60 drops of reagents. With this procedure, students determine the rate of reaction and the

  14. The influence of equilibrium chemical reactions on vapor-liquid phase diagrams

    SciTech Connect

    Barbosa, D.; Doherty, M.F.

    1986-01-01

    Phase diagrams for simultaneous chemical reaction and phase equilibrium are presented for ideal and non-ideal systems. It is shown that reactive-azeotropes can occur for ideal mixtures. The conditions for formation of reactive-azeotropes in constant volatility systems are derived. These conditions show that for such systems reactive-azeotropes can occur only when the volatiles of the reactants are either all higher or all lower than the volatilities of the products.

  15. Desalination of Thermal Water from Ixtapan De La Sal, Mex. By Means of Chemical Reactions, Ultrasound and Flotation Cell

    NASA Astrophysics Data System (ADS)

    Abrego, Josef.

    It is an excellent process because, the sodium chloride was converted into AgCl and calcium, sodium sulfate. The silver can be recovery from AgCl and from the final solution. Only it is necessary to design new tests in order to improve the time duration process and chemical reactive dose. Because for the equipment used, the process can be scaled to a largest seawater desalination. The bactericidal effect of the process and ultrasound is very important because the final water could be drinkable without harmful bacteria. Only spores and fungus remained 0.35% using ultrasound. The same process could be good for the seawater desalination because the chemical reactions are the same.

  16. General method and thermodynamic tables for computation of equilibrium composition and temperature of chemical reactions

    NASA Technical Reports Server (NTRS)

    Huff, Vearl N; Gordon, Sanford; Morrell, Virginia E

    1951-01-01

    A rapidly convergent successive approximation process is described that simultaneously determines both composition and temperature resulting from a chemical reaction. This method is suitable for use with any set of reactants over the complete range of mixture ratios as long as the products of reaction are ideal gases. An approximate treatment of limited amounts of liquids and solids is also included. This method is particularly suited to problems having a large number of products of reaction and to problems that require determination of such properties as specific heat or velocity of sound of a dissociating mixture. The method presented is applicable to a wide variety of problems that include (1) combustion at constant pressure or volume; and (2) isentropic expansion to an assigned pressure, temperature, or Mach number. Tables of thermodynamic functions needed with this method are included for 42 substances for convenience in numerical computations.

  17. Mixed-mode oscillations and chaos in return maps of an oscillatory chemical reaction

    NASA Astrophysics Data System (ADS)

    Blagojević, S. N.; Čupić, Ž.; Ivanović-Šašić, A.; Kolar-Anić, Lj.

    2015-12-01

    The return maps, as an element of mathematical phenomenology appropriate for general examinations of complex dynamic states of the oscillatory systems were used to detect and explain the evolution of mixed-mode oscillations and chaos in a six-dimensional nonlinear reaction system of the Bray-Liebhafsky (BL) reaction, a well-studied nonlinear chemical reaction system that exhibits complex dynamic behavior. For this purpose principally different Poincaré sections were applied and different transition scenarios between periodic and aperiodic states were examined by numerical simulations. It is shown that emergence of new periodic patterns can be detected by return maps already within chaotic windows. Besides, we also show that the higher dimensionality of manifold gives the impression of having several layers of manifolds.

  18. Inward Propagating Chemical Waves in a Single-Phase Reaction-Diffusion System

    NASA Astrophysics Data System (ADS)

    Shao, Xin; Wu, Yabi; Zhang, Jinzhong; Wang, Hongli; Ouyang, Qi

    2008-05-01

    We report our experimental and theoretical studies of inwardly propagating chemical waves (antiwaves) in a single-phase reaction-diffusion (RD) system. The experiment was conducted in an open spatial reactor using chlorite-iodide-malonic acid reaction. When the system was set to near Hopf bifurcation point, antiwaves appeared spontaneously, as predicted using both the reaction-diffusion (RD) equation and the complex Ginzburg-Landau equation (CGLE). Antiwaves change to ordinary waves when the system was moved away from the Hopf onset, which still agreed with RD simulations but could not be predicted by CGLE. We thus witnessed a new type of antiwave—wave exchange. Our analysis showed that this exchange occurred when the CGLE broke down as the system was far from the Hopf onset.

  19. Inward propagating chemical waves in a single-phase reaction-diffusion system.

    PubMed

    Shao, Xin; Wu, Yabi; Zhang, Jinzhong; Wang, Hongli; Ouyang, Qi

    2008-05-16

    We report our experimental and theoretical studies of inwardly propagating chemical waves (antiwaves) in a single-phase reaction-diffusion (RD) system. The experiment was conducted in an open spatial reactor using chlorite-iodide-malonic acid reaction. When the system was set to near Hopf bifurcation point, antiwaves appeared spontaneously, as predicted using both the reaction-diffusion (RD) equation and the complex Ginzburg-Landau equation (CGLE). Antiwaves change to ordinary waves when the system was moved away from the Hopf onset, which still agreed with RD simulations but could not be predicted by CGLE. We thus witnessed a new type of antiwave-wave exchange. Our analysis showed that this exchange occurred when the CGLE broke down as the system was far from the Hopf onset. PMID:18518496

  20. Drop-by-drop chemical reaction and sample introduction for capillary electrophoresis.

    PubMed

    Chen, Fengming; Rang, Ying; Weng, Ying; Lin, Luyao; Zeng, Hulie; Nakajim, Hizuru; Lin, Jin-Ming; Uchiyama, Katsumi

    2015-06-21

    In this paper, we report a novel sample introduction and chemical reaction strategy by drop-by-drop inkjet injection for an electrophoretically mediated microanalysis (EMMA). This method makes it possible to achieve an on-line introduction of reactant solutions by alternately ejecting small plugs, with an overlapping region of the plugs for mixing the reactants by electrophoresis, supporting chemical reactions, followed by electrophoretic separation of the final compounds. As a proof-of-concept of the method, the EMMA of an inkjetted mixture of 4-fluoro-7-nitrobenzofurazan (NBD-F) and amino acids was carried out as a model chemical reaction. The product NBD-amino acids were quantified by detection with laser induced fluorescence. The optimal conditions for the procedure were: inkjet driving voltage: +40-44 V; pulse width: 20-24 μs; drop-by-drop injection of reactant solutions: alternately 2 drops × 25 times for the amino acid solution and the NBD-F solution; zone overlapping voltage and time: 3 kV and 2 s; incubation time after overlapping: 5 min; separation voltage: 18 kV. Under the optimized conditions, a significant enhancement in sensitivity and a sensitive quantitative analysis were realized. The results obtained were comparable with those using the off-line labeling method. This method is rapid, cost-effective, and readily automated for EMMA. PMID:25728632